handbook of anti-tuberculosis agentstuberculosis (2008) 88(2) 85–86 introduction tuberculosis...

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Handbook of Anti-Tuberculosis Agents

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Aimsand ScopeTuberculosis is a speciality journal focusing on basic experimental researchon tuberculosis, notably on bacteriological, immunological and patho-genesis aspects. The journal publishes original research and reviews onthe host response and immunology of tuberculosis and the molecularbiology, genetics and physiology of the organism.Areas covered include:. immunology. immunogenetics. pathogenetics. microbiology. microbial physiology

. pathogenesis

. pathology

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TuberculosisCo-Editors in ChiefPatrick J. BrennanDepartment of Microbiology, Immunology and Pathology, College of Veterinary Medicine and Biomedical Sciences,

Colorado State University, Fort Collins, CO 80523-1682, USA

Douglas B.YoungCentre for Molecular Microbiology and Infection, 3.14 Flowers Building, South Kensington Campus, Imperial College,

London SW7 2AZ, UK

Deputy EditorBrian D. RobertsonCentre for Molecular Microbiology and Infection, 3.41 Flowers Building, South Kensington Campus, Imperial College

London SW7 2AZ, UK

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Section EditorsPeterAndersenStaens SeruminstitutCopenhagen, Denmark

Clifton Barry IIINational Institutes of HealthRockville, MD, USA

Warwick BrittonUniversity of SydneySydney, Australia

Phillip ButcherSt Georges, University of LondonLondon, UK

Sang-Nae ChoYonsei University College of MedicineSeoul, Korea

Ken DuncanBill and Melinda Gates FoundationSeattle, WA, USA

Kathleen EisenachUniversity of Arkansasfor Medical Sciences

Little Rock, AR, USA

Rajesh GokhaleNational Institute of ImmunologyNew Delhi, India

Glyn HewinsonVeterinary Laboratories AgencyWeybridge, UK

Bill JacobsAlbert Einstein College of MedicineYeshiva UniversityNew York, NY, USA

Gilla KaplanPublic Health ResearchInstitute, Newark, NJ, USA

Stefan KaufmannMax Planck Institute for Infec-tion Biology,Berlin, Germany

Mark PerkinsWorld Health OrganisationGeneva, Switzerland

Eric RubinHarvard School of PublicHealthBoston, MA, USA

David G RussellCornell UniversityIthaca, NY, USA

Consulting EditorA GinsbergGlobal Alliance for TB Drug DevelopmentNew York, USA

Editorial Advisory Board

A Apt ( Russia)G S Besra (UK)

W H Boom (USA)

S T Cole (France)

D Collins (New Zealand)

Q Gao (China)

MGonzalez-Juarrero (USA)

A Izzo (USA)

D Lewinsohn (USA)

DM McMurray (USA)

M Mitsuyama ( Japan)

V Mizrahi (South Africa)

I M Orme (USA)

L Schlesinger (USA)

T Shinnick (USA)

D van Soolingen (The Netherlands)

I Tsuyuguchi ( Japan)S Visweswariah (India)

RWallis (USA)

Tuberculosis (2008) 88(2) v

Contents

Introduction ..................................... 85

List of abbreviations ............................ 86

Amikacin ......................................... 87

Capreomycin .................................... 89

Clarithromycin .................................. 92

Clofazimine ..................................... 96

Cycloserine ...................................... 100

Ethambutol ...................................... 102

Ethionamide ..................................... 106

Gatifloxacin ..................................... 109

Isoniazid ......................................... 112

Kanamycin ....................................... 117

Levofloxacin ..................................... 119

Linezolid ......................................... 122

LL-3858 .......................................... 126

Moxifloxacin ..................................... 127

OPC-67683 ....................................... 132

PA-824 ........................................... 134

Para-aminosalicylic acid ........................ 137

Prothionamide .................................. 139

Pyrazinamide .................................... 141

Rifabutin ........................................ 145

Rifalazil .......................................... 148

Rifampin ......................................... 151

Rifapentine ...................................... 155

SQ109 ............................................ 159

Streptomycin .................................... 162

Thioridazine ..................................... 164

TMC-207 ......................................... 168

1472-9792/$ - see front matter © 2008 Elsevier Ltd. All rights reserved.

Disclaimer

The information compiled by the Global Alliance for TB Drug Development (TB Alliance) in the TB DrugDatabase is for research purposes only. This database is intended to provide a source of information aboutchemical compounds currently being used to treat TB, as well as additional compounds being examinedfor use in the future to treat TB.

It does not include information that has necessarily been considered or approved by any drug regulatoryauthority and should not be used by physicians to inform the prescribing of medication. Furthermore,no representation is made concerning the efficacy, safety, appropriateness or suitability of any of thechemical compounds contained in the TB Drug Database.

This information in the TB Drug Database has been compiled from numerous peer-reviewed studies. TheTB Alliance does not warrant that the information contained therein is accurate or complete and is notresponsible for any errors or omissions that may be found in such information or for results obtained fromthe use of such information.

You are encouraged to consult other sources and confirm the information contained in the TB DrugDatabase.

The TB Drug Database is a work in progress, with a goal to provide information for all the drugslisted below. If erroneous or otherwise inaccurate information is brought to the attention of theTB Alliance, a reasonable effort will be made to correct or delete. Please send your comments [email protected]

Tuberculosis (2008) 88(2) 85–86

IntroductionTuberculosis (TB), disproportionally affecting theworld’s poorest populations, remains one of thebiggest public health problems in the 21st century.The spread of multidrug-resistant TB (MDR-TB) andthe appearance of extensively drug-resistant TB(XDR-TB) pose new challenges for the prevention,treatment and control of this deadly disease. Thecontrol of TB is complicated by the fact that abouta third of the world’s population have latent TB,that is, they are infected with Mycobacteriumtuberculosis, the causative pathogen of TB, but areasymptomatic. About 10% of those latently infectedeventually develop active disease during their life-time. Although most of the M. tuberculosis-infectedindividuals remain asymptomatic, they serve asthe reservoir for the pathogen, making control ofthis disease a significant challenge. Infection bythe human immunodeficiency virus (HIV) markedlyenhances the rate of both new M. tuberculosisinfection and activation of latent infection. Thetreatment of HIV and M. tuberculosis coinfection isanother significant problem due to the difficulty ofthe coadministration of anti-TB and anti-HIV drugsas a result of drug drug interactions. Unfortunately,most drugs that are used today for the treatment ofTB were developed 40 or more years ago. Treatmentof TB is both lengthy and complicated. New regimensthat can shorten and simplify the treatment durationof active disease, that are effective against MDR-and XDR-TB, and that allow for coadministration withantiretroviral drugs are urgently needed.

The Global Alliance for TB Drug Development(TB Alliance) was founded in 2000 with the goalof developing new TB therapies that address thesignificant unmet medical needs in treating thisdisease. During the course of executing our drugdiscovery and development programs, we oftenneed to locate information about the existing drugsand drugs in development. We have found thatinformation relevant to TB drug research is veryscattered and frequently resides in decades-oldoriginal literature. There are few places wherecomprehensive data can be found on more than oneaspect of the various drugs. Many reviews coversingle topics in depth, concentrating, for example,

on comparisons of clinical options, animal modelsor physical characteristics. Researchers often needto spend a significant amount of time locatingimportant information as a comprehensive sourceof such data is lacking. Recognizing this need, theTB Alliance is developing a TB drug database asa resource for the TB drug research community.The materials published in this issue of Tuberculosisrepresent our initial effort towards this goal.

In this TB drug database, we attempt to bringtogether information on all approved drugs used totreat tuberculosis, on drugs in clinical developmentfor TB, and on some approved drugs being investi-gated for potential use in TB such as thioridazine. Atotal of 27 drugs are included in the current versionof the database. Referenced data include physicalcharacteristics, basic biology, efficacy and safety inhumans, and absorption, distribution, metabolismand excretion (ADME). However, this database isdesigned to be an overview of TB drug informationrather than an in-depth comprehensive review ofall aspects of TB treatment. For further informationon any specific compound or any specific aspect ofthese compounds, we suggest the reader use thisdatabase as a starting point for further literatureexploration.

This database is divided into sections on individualdrugs. References are provided with each drug. Inaddition, the following sources have been used:

DrugBank: http://redpoll.pharmacy.ualberta.ca/drugbank/FDA labels: these can be sometimes accessed viaDrugBank, alternatively through the FDA web siteat http://www.fda.gov/default.htmGoodman and Gilman’s The PharmacologicalBasis of Therapeutics, 10th Edition. Hardman J,Limbird L (editors), McGraw Hill publications.On-line at http://www.accessmedicine.com/resourceTOC.aspx?resourceID=28Merck Index: http://www.merckbooks.com/mindex/Physician’s Desk Reference: http://www.pdr.net/home/pdrHome.aspx


86 Introduction

The TB Alliance would like to acknowledge the manyindividuals who have contributed to the developmentof the TB drug database and this manuscript. Primaryinformation on the TB drugs was compiled and themanuscript drafted by Dr. Anne M. Gurnett and sum-mer intern Nelson Chiu. Dr. Zhenkun Ma, Dr. Ann M.Ginsberg and Dr. Melvin Spigelman were involved inthe conceptualization and design of the database.Dr. Zhenkun Ma, Dr. Khisi Mdluli, Dr. Priya Eddy andDr. Takushi Kaneko were involved in the editing andproofreading of the database and this publication.During the development of this manuscript, we havealso received valuable comments from various indi-viduals working for drug sponsors on their respective

compounds. These individuals are Dr. Karel De Beule(Tibotec, on TMC-207), Dr. Didier Leboulleux (sanofi-aventis, on rifapentine), Dr. Lawrence Geiter(Otsuka, on OPC-67683), and Dr. Marina Protopopova(Sequella, on SQ-109). Their valuable suggestions aregreatly appreciated. Finally, the TB Alliance wouldlike to acknowledge Dr. Patrick Brennan, editor ofTuberculosis, and Eelkje Sparrow together with otherindividuals from Elsevier for their help in making thisspecial issue possible.

Global Alliance for TB Drug Development80 Broad StreetNew York, NY 10004, USA

List of abbreviations

AMI Amikacin

CAP Capreomycin

CIP Ciprofloxacin

CLA Clarithromycin

CLOF Clofazimine

CYS Cycloserine

ETA Ethionamide

ETH Ethambutol

GATI Gatifloxacin

INH Isoniazid

KAN Kanamycin

LEV Levofloxacin

LIN Linezolid

MAC Mycobacterium avium complex

MDR Multidrug resistant

MIC Minimum inhibitory concentration

MOXI Moxifloxacin

MTB Mycobacterium tuberculosis

OFL Ofloxacin

PAS Para-aminosalicylic acid

PRO Prothionamide

PZA Pyrazinamide

RIF Rifampin

RIFAB Rifabutin

RIFAP Rifapentine

RIFAZ Rifalazil

STR Streptomycin

THZ Thioridazine

TMC TMC-207

XDR Extensively drug resistant

AMITuberculosis (2008) 88(2) 87–88

AmikacinGeneric and additional names: AmikacinCAS name: O-3-Amino-3-deoxy-a-d-glucopyranosyl-(16)-O-

[6-amino-6-deoxy-a-d-glucopyranosyl-(14)]-N1-[(2S)-4-amino-2-hydroxy-1-oxobutyl]-2-deoxy-d-streptamine

CAS registry #: 37517-28-5Molecular formula: C22H43N5O13Molecular weight: 585.60Intellectual property rights: GenericBrand names: Sulfate-Amiglyde-V (Fort Dodge); Amikin, Amiklin,

BB-K8, Biklin (Bristol-Myers Squibb); Lukadin (San Carlo);Mikavir (Salus); Novamin (Bristol-Myers Squibb); Pierami(Fournier)

NH2

NHHO

O

O

O

OH2N

HO

NH2

HOHO

HOO

OH

NH2

OH

OH

Polarity: Log P 9.048 [DrugBank]Formulation and optimal human dosage: Dose 1 g daily i.v. or intramuscularly (i.m.)1

Basic biology informationDrug target/mechanism: Amikacin (AMI), strepto-mycin (STR) and kanamycin (KAN) are all amino-glycosides. AMI inhibits protein synthesis by bindingtightly to the conserved A site of 16S rRNA in the 30Sribosomal subunit.1

Drug resistance mechanism: Ribosomal changes inthe 16S rRNA2 lead to possible cross-resistance withother class members, STR and KAN, but this isnot always complete. For example, KAN, AMI andcapreomycin (CAP) were still efficacious in vitrowhen resistance to STR had developed.3 See also theDrug resistance mechanism section for STR.In-vitro potency against MTB: MIC M. tuberculosis(H37Rv): 0.5 1mg/ml.4

Spectrum of activity: Aminoglycosides are usedmainly in infections involving aerobic, Gram-negative bacteria, such as Pseudomonas, Acineto-bacter and Enterobacter. Mycobacterium tubercu-losis is also sensitive to this drug. Gram-positivebacteria can also be treated with the drug but lesstoxic alternatives tend to be utilized. Synergisticeffects with the aminoglycosides and beta lactamshave resulted in use of this combination treatmentfor streptococcal infections, especially endocarditis[DrugBank].Other in-vitro activity: AMI showed bactericidalactivity against all the drug-sensitive clinical isolatesof M. tuberculosis tested and was superior to both

KAN and CAP, with bactericidal activity at 2mg/mlagainst 5 of 5 drug-resistant strains tested.4

AMI had no bactericidal activity, but did causesignificant reduction in bacterial load when M. tu-berculosis-infected macrophages were treated usingaminoglycosides; there was a 1 2 log reduction inCFU, 99% killing using STR 30mg/ml or KAN 30mg/mlor AMI 20mg/ml.4

In-vivo efficacy in animal model: AMI was the mostactive of the aminoglycosides tested (STR, AMI andKAN dosed at 200 mg/kg 6 times weekly) in a mousemodel of tuberculosis (2.3×107 CFU M. tuberculosisadministered i.v. followed by dosing 1 day later).STR reduced the CFU in the spleen by almost 1 log.All three drugs were less efficacious than Isoniazid(INH) at 25 mg/kg. All the mice in the drug-treatedgroups survived whereas the control mice died within30 days.5

Efficacy in humansEven though AMI showed the best in vivo activityamong the aminoglycosides it has not been widelyused clinically to treat tuberculosis probably dueto a combination of drug costs and toxicity.5

Although aminoglycosides remain important drugsfor treating diseases caused by M. tuberculosis(reviewed in Peloquin et al. 20046), they are nolonger first line. The aminoglycosides and CAP cannotbe administered orally.


88 Amikacin

Table 1

Species Half-life(h)

AUC(mg·h/l)

Cmax(mg/ml)

Volumedistribution(l/kg)

Clearance(ml/h)

PK methodology

Human 2.3 26±4 ~0.27 ~1.3 ml·min/kg 6.3±1.4 mg/kg dose given 3 timesdaily to steady state [Goodman &Gilman’s]

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Human: Chan et al. give a value for Cmax of

35 45mg/ml, with no dose given1

Human metabolic pathway: Primarily eliminatedthrough the kidney

Safety and TolerabilityAnimal toxicity: LD50 in mice of solutions pH 6.6,pH 7.4: 340 mg/kg, 560 mg/kg i.v. [Merck Index]Human drug drug interactions: Concurrent use ofother aminoglycosides and gentamycin, tobramycin,viomycin and cyclosporin is not recommended. AMIshould not be used with potent diuretics (ethacrynicacid or furosemide) as they can cause ototoxicity andmay increase the concentrations of AMI in tissues andserum [DrugBank].Human potential toxicity: The aminoglycosides andCAP are known for their ototoxicities, and incidencesmay be as high as 3 10%.1,5

Human adverse reactions: As with all aminoglyco-sides, toxic effects can occur due to effects tothe eighth cranial nerve resulting in hearing loss,loss of balance, or both. AMI primarily affectsauditory function. In addition neurotoxicity (muscle

paralysis and apnoea) and nephrotoxicity havebeen observed. In addition rashes, fever, headache,tremor, nausea, anaemia and hypotension have beenobserved [DrugBank].

References1. Chan E, et al. (2003) Pyrazinamide, ethambutol,

ethionamide, and aminoglycosides. In: Rom WN, Garay SM(editors), Tuberculosis, 2nd edition. Philadelphia, PA:Lippincott Williams & Wilkins, pp. 773 789.

2. Di Perri G, Bonora S (2004) Which agents should we usefor the treatment of multidrug-resistant Mycobacteriumtuberculosis? J Antimicrob Chemother 54, 593 602.

3. Ho Y, et al. (1997) In-vitro activities of aminoglycosideaminocyclitols against mycobacteria. J AntimicrobChemother 40, 27 32.

4. Rastogi N, et al. (1996) In vitro activities of fourteenantimicrobial agents against drug susceptible and resistantclinical isolates of Mycobacterium tuberculosis andcomparative intracellular activities against the virulentH37Rv strain in human macrophages. Curr Microbiol 33,167 175.

5. Lounis N, et al. (1996) Which aminoglycoside orfluoroquinolone is more active against Mycobacteriumtuberculosis in mice? Antimicrob Agents Chemother 41,607 10.

6. Peloquin C, et al. (2004) Aminoglycoside toxicity:daily versus thrice-weekly dosing for treatment ofmycobacterial diseases. Clin Infect Dis 38, 1538 44.

CAP

Tuberculosis (2008) 88(2) 89–91

CapreomycinGeneric and additional names: Capreomycin sulfateCAS name: 3,6-diamino-N-[[(8E)-15-amino-11-

(2-amino-3,4,5,6-tetrahydropyrimidin-4-yl)-8-[(carbamoylamino)methylidene]-2-(hydroxymethyl)-3,6,9,12,16-pentaoxo-1,4,7,10,13-pentazacyclohexadec-5-yl]methyl]hexanamidesulfuric acid

CAS registry #: 11003-38-6Molecular formula: C25H46N14O12SMolecular weight: 766.786Intellectual property rights: Generic. Polypeptide

antibiotic isolated from Streptomyces capreolus.Brand names: Capastat, Capastat sulfate,

Capreomycin, Capreomycin sulphate, Ogostal,Capreomycin IA, Capreomycin IB

NH

NH

HN

HN

NH

NH2

OR

H2N

O

O

O

O NH2

NH

NH

NH

H

NH NH2

O

O

CapreomycinIA (R = OH),IB (R = H)

Solubility: Soluble in water. Practically insoluble in most organic solvents [Merck Index].Polarity: pKa in 66% aqueous DMF: 6.2, 8.2, 10.1, 13.3 [Merck Index]. Log P 9.609 [DrugBank].Stability: Stable in aqueous solution at pH 4 8; unstable in strongly acidic or strongly basic solutions

[Merck Index].Formulation and optimal human dosage: 1 g vial, 1 g daily, i.v. or intramuscularly (i.m.)

Basic biology informationDrug target/mechanism: Capreomycin (CAP) is apolypeptide antibiotic [FDA label]. The mode ofaction is not fully understood although CAP clearlyinteracts with the ribosome and inhibits proteinsynthesis. A gene-chip experiment in Mycobacteriumtuberculosis demonstrated the up-regulation ofseveral ribosomal proteins (e.g. RpsR, RplI, RplYand RplJ), Rv2907c (16S rRNA processing protein)and Rv1988 (methyltransferase). The expressiondata support the interaction of CAP with ribosomalcomponents although a number of genes unrelatedto protein synthesis are also affected.1 As CAPhas such potent activity against the persistentforms of TB the drug may have a target orsecondary target outside the ribosome; the gene-chip data may lead to discovery of new targetsfor CAP.1

Drug resistance mechanism: Resistance is associatedwith ribosomal changes in the 16S rRNA;2 there ispossible cross-resistance with streptomycin (STR),but this is not always complete. For example,kanamycin (KAN), amikacin (AMI) and CAP were still

efficacious in vitro when resistance to STR haddeveloped.3 In addition, CAP was still efficaciousin vitro in several strains resistant to STR, AMIand KAN.3 It has been shown that one mecha-nism of resistance to CAP is via inactivation ofa ribosomal methylase TlyA. Interestingly, manybacteria lack tlyA and may be naturally resistant toCAP through this mechanism.4 No cross-resistancehas been observed between CAP and isoniazid(INH), aminosalicylic acid, cycloserine (CYS), ethion-amide (ETA), or ethambutol (ETH) [DrugBank].See also the Drug resistance mechanism sectionfor STR.In-vitro potency against MTB: MIC M. tuberculosis(H37Rv): 2mg/ml.5

Spectrum of activity: CAP is active against M. tuber-culosis and M. avium.Other in-vitro activity: It has been demonstratedthat CAP has bactericidal activity against non-replicating forms of M. tuberculosis equal only tometronidazole.6 The treatment of M. tuberculosiswithin macrophages using aminoglycosides and CAPresulted in ~1 log reduction in CFU at day 7 using


90 Capreomycin

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Mouse 0.18±0.05 34±6.4 94±19(15 minutespost dose)

I.V. injection of 120 mg/kg CAP8

Human 32(range 20 47)

Dose: 1 g CAP i.m.

STR (30mg/ml), CAP (30mg/ml), KAN (30mg/ml) andjust greater than a 2 log reduction at day 7 withAMI (20mg/ml).5 The MBC/MIC ratio of 2 for CAP issimilar to that for STR, KAN and AMI.7

In-vivo efficacy in animal model: CAP and CAPliposome formula showed efficacy against M. aviumin the beige mouse model.8 Klemens et al. showedmodest activity of CAP (150 mg/kg) in a mousemodel against a clinically resistant isolate ofM. tuberculosis.9

Efficacy in humansThe aminoglycosides and CAP cannot be adminis-tered orally. CAP is recommended for pulmonaryinfections caused by CAP-susceptible M. tuberculosiswhen primary agents [INH, rifampin (RIF), ETH,aminosalicylic acid, and STR] have been ineffective[DrugBank]. CAP has been administered as asecondary TB treatment for more than 25 years,but its use is limited due to renal and auditorytoxicities.

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Mouse: Spleen, kidney and lung AUC values after

i.v. injection of 120 mg/kg CAP to mice were 184,982 and 60mg·h/ml, respectively.8

• Human: Not bioavailable via oral administration.Higher Cmax when given i.m. compared withi.v. Low serum concentrations at 24 hours. Noaccumulation after 30 days at a dose of 1 g/day[FDA label].

Human metabolic pathway: CAP is excreted in urinewith 52% as the unchanged drug excreted in 12 hours.Urine concentration averaged 1.68mg/ml during the6 hours following a 1-g dose. It is not known if CAPis excreted in human milk [DrugBank].

Safety and TolerabilityAnimal toxicity: LD50 in mice, rats (mg/kg): 250, 325i.v.; 514, 1191 s.c., [Merck Index]In teratology studies, a low incidence of “wavy ribs”was noted in litters of female rats treated with50 mg/kg daily of CAP [FDA label].

Animal safety pharmacology: Renal and eighth-cranial-nerve toxicity; cataracts developed in 2 dogson doses of 62 mg/kg and 100 mg/kg for prolongedperiods.Human drug drug interactions: Other parenteralantituberculosis agents (e.g. STR) have similar toxiceffects, particularly on cranial nerve and renalfunction, and simultaneous administration of theseagents with CAP is not recommended. Skin rasheswere reported when CAP and other antituberculosisdrugs were given together [FDA label].There is an increased risk of damage to the kidneysand ears if capreomycin is taken with vancomycin,cisplatin, or aminoglycoside antibiotics.There is an increased risk of kidney damage ifcapreomycin is taken with colistin.Human potential toxicity: CAP demonstrates manyof the auditory side effects in common with theaminoglycosides. In addition it is associated withrenal effects due to kidney tubulopathy leading to al-kalosis.2 In 36% of 722 CAP-treated patients elevationof blood urea nitrogen (BUN) above 20 mg/100 mlwas observed [FDA label]. BUN elevation or anyrenal damage indicates that CAP dosage shouldbe reduced or discontinued [FDA label]. Periodicdeterminations of liver function are recommendedduring CAP treatment. Leukocytosis and leukopeniahave been observed. Most patients have eosinophiliaexceeding 5% while receiving daily injections ofCAP; this decreased with reduction of the CAPdosage to 2 or 3 g weekly. Signs of potential sideeffects, especially nephrotoxicity; hypersensitivity;hypokalemia; neuromuscular blockade; auditory andvestibular ototoxicity; and pain, hardness, unusualbleeding, or a sore at the place of injection[FDA label].Human adverse reactions: Pain and excessivebleeding at the injection site have been reported,sterile abscesses have been noted, and rare cases ofthrombocytopenia [DrugBank].Possible side effects are blood disorders, rash(allergic reaction), hearing disturbances, damage tothe kidneys, alteration in results of liver functiontests and disturbances in the levels of chemicalcomponents (electrolytes) in the blood.

CAP

Capreomycin 91

References1. Fu L, Shinnick T (2007) Genome-wide exploration of

the drug action of capreomycin on Mycobacteriumtuberculosis using Affymetrix oligonucleotide GeneChips.J Infect 54, 277 84.



4. Johansen S, et al. (2006) Capreomycin binds acrossthe ribosomal subunit interface using tlyA-encoded2′-O-methylations in 16S and 23S rRNAs. Mol Cell 23,173 82.

5. Rastogi N, et al. (1996) In vitro activities of fourteenantimicrobial agents against drug susceptible and resistantclinical isolates of Mycobacterium tuberculosis and

comparative intracellular activities against the virulentH37Rv strain in human macrophages. Curr Microbiol 33,167 175.

6. Heifets L, et al. (2005) Capreomycin is active against non-replicating M. tuberculosis. Ann Clin Microbiol Antimicrob4, 6.

7. Heifets L, Lindholm-Levy P (1989) Comparison of bacte-ricidal activities of streptomycin, amikacin, kanamycin,and capreomycin against Mycobacterium avium andM. tuberculosis. Antimicrob Agents Chemother 33, 1298303.

8. Le Conte P, et al. (1994) Pharmacokinetics, toxicity,and efficacy of liposomal capreomycin in disseminatedMycobacterium avium beige mouse model. AntimicrobAgents Chemother 38, 2695 701.

9. Klemens S, et al. (1993) Therapy of multidrug-resistanttuberculosis: lessons from studies with mice. AntimicrobAgents Chemother 37, 2344 7.

Tuberculosis (2008) 88(2) 92–95

ClarithromycinGeneric and additional names: ClarithromycinCAS name: 6-O-MethylerythromycinCAS registry #: 81103-11-9Molecular formula: C38H69NO13Molecular weight: 747.95Intellectual property rights: GenericBrand names: Biaxin (Abbott); Clathromycin (Taisho); Cyllind (Abbott);

Klacid (Abbott); Klaricid (Abbott); Macladin (Guidotti); Naxy (SanofiWinthrop); Veclam (Zambon); Zeclar (Abbott)

Solubility: Clarithromycin is soluble in acetone, slightly soluble inmethanol, ethanol, and acetonitrile, and practically insoluble in water[FDA label]. Water solubility 0.33 mg/l [DrugBank].

Polarity: Log P 2.69 [DrugBank]. Other authors have obtained values ofLog P= 1.7 at pH 7.4.1

Acidity/basicity: pKa 8.99 [DrugBank]Melting point: 217 220ºC [DrugBank]

O

O

O

M

M

e

e

O

O

Me

MeMe

OHHO

Me

Me

O

N

M

M

e

e

HO

Me Me

OMe

O

OH

Me

OMe

Formulation and optimal human dosage: Biaxin is available as immediate-release tablets, extended-releasetablets, and granules for oral suspension.Each Biaxin tablet contains 250 mg or 500 mg of clarithromycin.After constitution, each 5 ml of Biaxin suspension contains 125 mg or 250 mg of clarithromycin.Dose 250 1000 mg daily, higher amounts given in multiple doses [FDA label].

Basic biology informationDrug target/mechanism: Clarithromycin (CLA), amacrolide antibiotic similar to erythromycin andazithromycin, binds to the 50S ribosomal subunit re-sulting in inhibition of protein synthesis [DrugBank].Drug resistance mechanism: Macrolide resistanceis commonly caused by ErmB-driven methylationof the 23S rRNA resulting in a substantial lossin drug binding. Mycobacterium tuberculosis andM. smegmatis are both intrinsically resistant tothe macrolides, and resistance can be induced inboth species.2,3 In M. tuberculosis the ermB genewas upregulated up to 30× baseline when bacteriawere incubated with the drug; induction followeda bell-shaped curve with maximum upregulation at2 4mg/ml.2 Newer macrolides with lower MICs forM. tuberculosis have been reported4 and detailsabout the induction of ermB with these analogs willbe informative.Other bacterial resistance: most strains of meticillin-resistant and oxacillin-resistant staphylococci areresistant to CLA [FDA label]. About 3.5% of

Helicobacter pylori strains tested were resistant toCLA; treatment of H. pylori infections with CLA alonewas not recommended due to risk of unacceptablerates of resistance development [FDA label].In-vitro potency against MTB: MIC M. tuberculosis(H37Rv): 8mg/ml at pH 7.4.5

MIC against a panel of M. tuberculosis clinicalisolates was 1.3 10mg/ml compared with >10mg/mlfor erythromycin.6

Spectrum of activity: CLA has relatively poor in vitroactivity against M. tuberculosis but has betteractivity against M. avium (MIC90 8mg/ml), andM. kansasii (MIC90 �0.5mg/ml). In fact the authorsconclude that CLA could be useful for treatmentof the slowly growing nontuberculous mycobacteriawith the exception of M. simiae.7 CLA is 8 32-foldmore active than erythromycin against M. avium.1

CLA is active in vitro against a variety of aerobicand anaerobic Gram-positive and Gram-negativemicroorganisms as well as most microorganismsof the M. avium complex (MAC). The 14-OHCLA metabolite has antimicrobial activity with a


CLA

Clarithromycin 93

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Mouse 13.3 16.83 3.74 200 mg/kg single oral dose inneutropenic mice18

Human 2.33 2.99±1.97 0.6±0.43 386±332 198±98 ml/min 200 mg single oral dose average in39 healthy human volunteers19

somewhat different spectrum from the parent;for example, with M. avium isolates the 14-OHmetabolite is 4 7 times less active than CLA.CLA has in vitro and clinical activity againstStaphylococcus aureus, Streptococcus pneumoniae,Str. pyogenes, Haemophilus influenzae, H. parain-fluenzae, Moraxella catarrhalis, Mycoplasma pneu-moniae, Chlamydia pneumoniae, M. avium andM. intracellulare. CLA has in vitro activity, butuntested clinical activity, against streptococci,Bordetella pertussis, Legionella pneumophila, Pas-teurella multocida, Clostridium perfringens andPropionibacterium acnes [FDA label].Other in-vitro activity: CLA has been reportedto be inactive against M. tuberculosis withMICs 64 128mg/ml against clinical isolates.8 How-ever others have indicated that MICs, thoughhigh, can be measured.9,10 Nine M. tuberculosisstrains resistant to isoniazid (INH)/rifampin (RIF)/streptomycin (STR)/ethambutol (ETH) were exam-ined for CLA MICs: 4 strains >16mg/ml, 2 strains with16mg/ml and 2 strains with 2mg/ml.11 A substantialnumber of reports describe in vitro synergy of CLAwith various first-line TB drugs and with antibioticsthat inhibit cell-wall biosynthesis. CLA had little orno synergy with INH or RIF alone but significantsynergy when INH/RIF/CLA were tested together12

and with the combination INH/RIF/ETH/CLA.13 ETHenhanced CLA activity in all the clinical isolatestested, as did DMSO and Tween 80, indicatingthat this enhancement may result from cell-walldamage resulting in better penetration of CLA intothe mycobacterium; synergy with vancomycin wasalso demonstrated.10 Conflicting results have beenreported for CLA effects on M. tuberculosis-infectedmacrophages, especially with regard to synergy. Onegroup reported synergy when M. tuberculosis wascultured in macrophages with CLA and pyrazinamide(PZA) with a FIC (fractional inhibitor concentration)of 0.5; when CLA was mixed with RIF the FICwas 1 indicating an additive effect.14 Howeverothers reported synergy when M. tuberculosis-infected macrophages were treated with CLA andRIF.15 High intracellular drug concentration of CLA inmacrophages was observed.14 CLA was active against

M. avium complex in mouse and human macrophagecell culture [FDA label].In-vivo efficacy in animal model: In vivo studies usinga mouse model of M. tuberculosis (H37Rv) showedweak efficacy with CLA but the drug did protect micefrom tuberculosis-induced mortality; CLA (200 mg/kgdaily) had significantly poorer efficacy than INH(25 mg/kg daily) when mice were treated forup to 8 weeks.15 In the same mouse modelCLA (200 mg/kg) was slightly more efficacious thanthiacetazone (60 mg/kg); in combination studiesCLA and INH (25 mg/kg) were more active thanINH and thiazoacetone or INH and STR (200 mg/kg).15

Further studies on the activity of CLA with variousdrug combinations are needed. CLA was moreeffective against M. avium in vivo comparedwith erythromycin and amikacin and equal toamikacin (AMI)/ETH/RIF and CLA/AMI.1

Efficacy in humansPublished data on CLA treatment for TB in humansare scarce, although several reviews advocate itsuse.16,17 CLA is approved for use for the follow-ing: upper respiratory tract infections, sinisititis,bronchitis exacerbation due to Haemophilus spp.and Moraxella, community-acquired pneumonia,uncomplicated skin and skin structure, duodenalulcers, and disseminated mycobacterial infectionswith M. avium or M. intracellulare. Patients takingCLA 500 mg twice daily for ~11 months for thetreatment of MAC were 69% less likely to exhibitMAC bacteremia and a significant survival rate wasmanifested [FDA label]. CLA is approved for use inchildren above 6 months and in geriatric populations,with no special treatment recommended for thesegroups.

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Rat: PK of CLA in rats is superior to that of ery-

thromycin, with 15 73 times higher concentrationsin plasma and tissues; the peak level of CLA in lungwas especially high.20

• Human: PK of 14-OH metabolite is not linear withparent drug.19 Bioavailability is ~50% [FDA label].

94 Clarithromycin

CLA is 70% plasma bound.18 Steady-state peakplasma CLA concentrations of 1 2mg/ml werereached in 2 3 hours with a 250-mg doseadministered every 12 hours, and 3 4mg/ml witha 500-mg dose administered every 8 12 hours. Nosignificant differences in steady-state drug levelswere seen with hepatic impaired or AIDS patientscompared to healthy subjects. Extended-releasetablets resulted in lower and later steady-statepeak but equivalent AUCs [FDA label].Good tissue penetration with 5 times more drug inlung compared with plasma and penetration intothe middle ear [FDA label].

Human metabolic pathway: CLA is first metabolizedto 14-OH CLA. The elimination half-life for CLA is 3 4hours with 250 mg twice daily, and 5 7 hours with500 mg 2 3 times daily. CLA is mainly excreted byliver and kidney, 30 40% excreted in urine dependingon dose, an additional 10% excreted in urine as activemetabolite, 14-OH CLA. It is not known if CLA isexcreted into human milk [FDA label].

Safety and TolerabilityAnimal toxicity: LD50 of CLA i.v. in mice was184 mg/kg and 227 mg/kg in two separate studies.This was several times higher than the LD50 inrats (64 mg base/kg). These values were lower thanthose obtained following administration to mice byother routes. Signs of toxicity in both species weredecreased activity, ataxia, jerks, tremors, dyspneaand convulsions.21

Adverse effects were found on fetal development inmonkeys, rats and mice; serum drug concentrationsin the foetus are significantly higher than those inthe mother [FDA label].Hepatotoxicity occurred in all species tested (dog,rat, monkey): in rats and monkeys at doses 2 timesgreater than, and in dogs at doses comparable to,the maximum human daily dose [FDA label].Renal tubular degeneration, testicular atrophy,corneal opacity and lymphoid depletion were allobserved in animal testing [FDA label].Human drug drug interactions: CLA inhibits cy-tochrome CYP3A4 and P-glycoprotein. Concomitantadministration of CLA with cisapride, pimozide,or terfenadine is contraindicated due to cardiacarrhythmias (QT prolongation, ventricular tachy-cardia, ventricular fibrillation, and torsades depointes) probably because of inhibition of hepaticmetabolism of these drugs. Fatalities have beenreported. Concomitant dosing of astemizole is notrecommended for similar reasons and because ofclinical experience with erythromycin [FDA label].Human potential toxicity: CLA should not be usedduring pregnancy due to adverse effects seen in fetaldevelopment in monkeys, rats and mice.

Hepatotoxicity: increased liver enzymes, and hep-atocellular and/or cholestatic hepatitis, with orwithout jaundice. Hepatic dysfunction may be severebut is usually reversible [FDA label].Cardiac: QT prolongation and ventricular arrhyth-mias, including ventricular tachycardia and torsadesde pointes, have been associated with CLA [FDA la-bel].Hypoglycaemia occurs in rare cases [FDA label].Human adverse reactions: Reactions are generallymild and the drug is well tolerated especially withslow-release tablets of Biaxin. In phase-1 clinicaltrials CLA appears to be safe and well tolerated upto 1200 mg/day as single oral dose.19

Adverse effects most commonly seen were gastroin-testinal (diarrhoea, vomiting, abdominal pain andnausea), headache, and rash [FDA label].

References

1. Fernandes P, et al. (1989) In vitro and in vivo activities ofclarithromycin against Mycobacterium avium. AntimicrobAgents Chemother 33, 1531 4.

2. Andini N, Nash K (2006) Intrinsic macrolide resistanceof the Mycobacterium tuberculosis complex is inducible.Antimicrob Agents Chemother 50, 2560 2.

3. Nash K (2003) Intrinsic macrolide resistance inMycobacterium smegmatis is conferred by a novelerm gene, erm(38). Antimicrob Agents Chemother 47,3053 60.

4. Falzari K, et al. (2005) In vitro and in vivoactivities of macrolide derivatives against Mycobacteriumtuberculosis. Antimicrob Agents Chemother 49, 1447 54.


6. Gorzynski E, et al. (1989) Comparative antimycobac-terial activities of difloxacin, temafloxacin, enoxacin,pefloxacin, reference fluoroquinolones, and a newmacrolide, clarithromycin. Antimicrob Agents Chemother33, 591 2.

7. Brown B, et al. (1992) Activities of clarithromycinagainst eight slowly growing species of nontuberculousmycobacteria, determined by using a broth microdilutionMIC system. Antimicrob Agents Chemother 36, 1987 90.

8. Truffot-Pernot C, et al. (1995) Clarithromycin is inactiveagainst Mycobacterium tuberculosis. Antimicrob AgentsChemother 39, 2827 8.

9. Rodriguez- Diaz J, et al. (2003) Synergic activity offluoroquinolones and linezolid against Mycobacteriumtuberculosis. Int J Antimicrob Agents 21, 354 6.

10. Bosne-David S, et al. (2000) Intrinsic resistanceof Mycobacterium tuberculosis to clarithromycin iseffectively reversed by subinhibitory concentrations ofcell wall inhibitors. J Antimicrob Chemother 46, 391 5.

11. Hoffner S, et al. (1997) In-vitro activity of fluorinatedquinolones and macrolides against drug-resistant My-cobacterium tuberculosis. J Antimicrob Chemother 40,885 8.

CLA

Clarithromycin 95

12. Bhusal Y, et al. (2005) Determination of in vitro synergywhen three antimicrobial agents are combined againstMycobacterium tuberculosis. Int J Antimicrob Agents 26,292 7.

13. Cavalieri S, et al. (1995) Synergistic activities of clar-ithromycin and antituberculous drugs against multidrug-resistant Mycobacterium tuberculosis. Antimicrob AgentsChemother 39, 1542 5.

14. Mor N, Esfandiari A (1997) Synergistic activities ofclarithromycin and pyrazinamide against Mycobacteriumtuberculosis in human macrophages. Antimicrob AgentsChemother 41, 2035 6.

15. Luna-Herrera J, et al. (1995) Antituberculosis activityof clarithromycin. Antimicrob Agents Chemother 39,2692 5.

16. Chan E, Iseman M (2002) Current medical treatment fortuberculosis. Br Med J 325, 1282 6.


18. Hoffman H, et al. (2003) Influence of macrolide suscep-tibility on efficacies of clarithromycin and azithromycinagainst Streptococcus pneumoniae in a murine lunginfection model. Antimicrob Agents Chemother 47,739 46.

19. Chu S, et al. (1992) Pharmacokinetics of clarithromycin,a new macrolide, after single ascending oral doses.Antimicrob Agents Chemother 36, 2447 53.

20. Kohno Y, et al. (1989) Comparative pharmacokinetics ofclarithromycin (TE-031), a new macrolide antibiotic, anderythromycin in rats. Antimicrob Agents Chemother 33,751 6.

21. http://www.medsafe.govt.nz/Profse/Datasheet/k/KlacidIVinj.htm

Tuberculosis (2008) 88(2) 96–99

ClofazimineGeneric and additional names: 3-(p-chloroanilino)-10-(p-chlorophenyl)-

2,10-dihydro-2-(isopropylimino)phenazine; 2-(4-chloroanilino)-3-isopropylimino-5-(4-chlorophenyl)-3,5-dihydrophenazine; 2-p-chloroanilino-5-p-chlorophenyl-3,5-dihydro-3-isopropyliminophenazine

CAS name: N,5-bis(4-chlorophenyl)-3-(1-methylethylimino)-5H-phenazin-2-amine

CAS registry #: 2030-63-9Molecular formula: C27H22Cl2N4Molecular weight: 473.40Intellectual property rights: Generic. Clofazimine was first synthesized

in 1954 as an anti-tuberculosis lichen-derived compound. The drugwas thought to be ineffective against tuberculosis but in 1959 Changdemonstrated its effectiveness against leprosy. After clinical trials theproduct was launched in 1969 as Lamprene. Marketed by Novartis asLamprene.

N

N N

NH

Cl

Cl

MeMe

Brand names: Lampren(e) (Novartis)Derivatives: Riminophenazine analogs B4154 and B 4157.1

Solubility: Soluble in dilute acetic acid, DMF. Soluble in 15 parts of chloroform, 700 parts of ethanol, 1000parts of ether. Practically insoluble in water [Merck Index].

Polarity: Log P 7.132 [DrugBank]Acidity/basicity: pKa 8.51 [DrugBank]Melting point: 210 212ºC [DrugBank]Formulation and optimal human dosage: Lamprene, 50 mg clofazimine. Daily dose 1 2 tablets (50 100 mg).2

Clofazimine is a substituted iminophenazine bright-red dye.

Basic biology informationDrug target/mechanism: The mode of action ofclofazimine (CLOF) is not defined. Studies have im-plicated membrane perturbations3 in Staphylococcusaureus, inhibition of phospholipase A24 and effectson potassium transporters.5 Metabolic labeling isnot specifically inhibited3 and it is antagonizedby tocopherol and lysophospholipase A.6 CLOF hasa high redox potential ( 0.17 V at pH 7) andmay result in generation of hydrogen peroxide.7,8

Transcriptional analysis demonstrated that CLOFclustered with known respiratory modulators suchas phenothiazines, cyanide and azide. This indicatesthat it may inhibit bacterial cell growth byinterfering with electron transport.9

Drug resistance mechanism: Laboratory and clinicalmutants have been difficult to generate. Thereis some controversy about activity against specificrifampin (RIF)- and isoniazid (INH)-resistant strains

(see Other in-vivo activity section). In Mycobac-terium leprae Lamprene does not show cross-resistance with dapsone or RIF.In-vitro potency against MTB: MIC M. tuberculosis(H37Rv): 0.1mg/ml.10

Spectrum of activity: Lamprene is described asmycobacteria specific [FDA label] while CLOF MICsof �1mg/ml have been reported for staphylococci,Streptomyces species, bacilli and Listeria.6

Other in-vitro activity: CLOF MICs were found byDe Logu et al. to be higher against RIF- andpyrazinamide (PZA)-resistant M. tuberculosis strainscompared to wild type (WT) (M. tuberculosis MICs:H37Rv 0.78m/ml; PZA-resistant 6.25mg/ml; RIF-resistant 6.25mg/ml; INH-resistant 0.39mg/ml),11

however Reddy et al.1 showed sensitivity againstINH-, RIF- and ethambutol (ETH)-resistant strains(M. tuberculosis MICs: H37Rv 0.12m/ml; multidrug-resistant (MDR) 0.12 2mg/ml; RIF-resistant 0.25


CLOF

Clofazimine 97

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Human 70 days afterprolongedtreatment

1.5* 0.145* *200 mg fasting oral dose20

(administered with PAS, cycloserine,ETH and pyridoxime), Tmax 6.23 h.

0.5mg/ml; INH-resistant 0.12mg/ml).1 Both agreethat INH-resistant strains generally remain sensitiveto CLOF but there may be some increases inthe MICs for RIF-resistant, PZA-resistant and MDRstrains. CLOF and one analog showed efficacy againstM. tuberculosis-infected macrophages with activityat 0.5mg/ml equivalent to that of INH at 0.1mg/ml;another analog was less effective.1 Possible synergywith INH has been reported.12 CLOF was foundbactericidal.3

In-vivo efficacy in animal model: Early experimentswith CLOF in tuberculosis models showed efficacy inhamsters and mice with less activity in monkeys andguinea pigs (reviewed in Reddy et al. 19961). Thecompound was virtually abandoned for tuberculosisbut eventually developed for use in leprosy. MDR-TBrenewed interest in the compound and in 1996efficacy was demonstrated in M. tuberculosis-infected mice with weekly dosing 3 days postinfection continuing for 12 weeks. No organisms wererecovered from lungs although spleens still showedsigns of infection. In the same model some efficacywas observed with once and twice weekly dosing.1

Liposome-encapsulated drugs tend to accumulatein macrophages and are released at slower ratesthan the free counterpart (reviewed in Adams et al.199913) and have been described as less toxic to cellsin vitro and in vivo.14 Using a mouse model rep-resenting acute, established and chronic M. tuber-culosis infection significant efficacy with liposome-encapsulated CLOF was demonstrated. Free CLOFwas maximally tolerated at 5 mg/kg in mice at whichdose it was ineffective; encapsulated CLOF wasused at 50 mg/kg and showed efficacy and no signsof toxicity.13 Nanosuspension for use with i.v. for-mulation of CLOF was as efficacious as liposomeencapsulation.15 While these experiments do suggestthat encapsulating drug can reduce toxicity, themaximum drug dose tolerated in mice was reportedas 5 mg/kg whereas others have found 20 mg/kg andhigher tolerable doses in the same animal (compareReddy et al. 19961 and Adams et al. 199913).Controversy about drug carry-over in animal modelsclouds simple interpretation of some of the reportedin-vivo activity.16

In addition to its antimicrobial activity, the drughas other pharmacological activity such as its anti-

inflammatory effects, pro-oxidative activity andimmunopharmacological properties.8

Efficacy in humansCLOF is recommended as a second-line compoundfor use in combination with other drugs for thetreatment of drug-resistant tuberculosis (reviewedin Mukherjee et al. 200417 and du Toit et al. 200618).Treatment of human tuberculosis patients with CLOFin combination with LIN and other drugs has beendescribed.2 CLOF was first launched by Novartis asLamprene in 1969 as an anti-leprosy agent (reviewedin Sansarricq 200419).

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Rat: High levels (1 3.6 mg/g wet weight tissue)

were observed in rat tissue having reticulo-endothelial components following oral treatmentof 20 mg/kg for several months;21 other tissues hadrelatively low drug levels (range 3 114mg/g of wettissue).

• Human: 45 62% oral absorption rate. The averageserum concentrations in leprosy patients treatedwith 100 mg and 300 mg daily were 0.7mg/mland 1.0mg/ml, respectively (Lamprene FDA label).CLOF is highly lipophilic and tends to be depositedpredominantly in fatty tissue and in cells ofthe reticuloendothelial system [FDA label]. CLOFconcentrates in macrophages, and serum levelsare often low or undetectable.1 Cannot be giveni.v. unless formulated (Adams et al. 1999,13

reviewed in Peters et al. 200022). A high-fatmeal increases bioavailability but intra-subjectvariation needs to be examined more carefully.20

Human metabolic pathway: CLOF half-life followingrepeated oral doses is minimally 70 days; in a 24-hour (post 300 mg dose) urine collection parentdrug or metabolites were negligible. Lamprenepasses into breast milk. Metabolism of Lamprene ishepatic. Three metabolites have been identified butit is unclear if metabolites are pharmacologicallyactive. Metabolite I: hydrolytic dehalogenation ofCLOF; metabolite II: hydrolytic deamination reactionfollowed by glucuronidation; metabolite III: probablya hydroxylated CLOF glucuronide. Absorption varies

98 Clofazimine

from 45% to 62% following oral administration inleprosy patients. Food increases bioavailability andrate of absorption (Lamprene FDA label).Crystalline deposits of the drug have been seen atautopsy in mesenteric lymph nodes, adrenals, sub-cutaneous fat, liver, bile, gall bladder, spleen, smallintestine, muscles, bones, and skin [FDA label].

Safety and TolerabilityAnimal toxicity: Acute toxicity: LD50 orally in mice,rats, and guinea pigs: >4 g/kg; in rabbit: 3.3 g/kg.CLOF toxicity has been decreased by the use ofliposome-encapsulated drug with no reported changein the MIC.14

Reproductive toxicity: At 25 times normal humandose CLOF impaired fertility in rats; fetal toxicityin mice was found at 12 25 times normal humandose, i.e., retardation of fetal skull ossification,increased incidence of abortions and stillbirths, andimpaired neonatal survival. The skin and fatty tissueof offspring became discolored approximately 3 daysafter birth, which was attributed to the presence ofLamprene in the maternal milk (Reddy et al. 19998

and FDA label).Genotoxicity: CLOF was Ames negative but inhibitedgrowth of human fibroblasts at 2.5mg/ml, showeddose-related changes in mitotic indexes, and showedelevated incidence of chromosomal aberrationsin mice treated with 40 mg/kg daily for sevendays.23,24

No long-term carcinogenicity studies in animals havebeen conducted with Lamprene. Lamprene was notteratogenic in laboratory animals at dose levelsequivalent to 8 times (rabbit) and 25 times (rat) theusual human daily dose.Animal safety pharmacology: Elevated levels of albu-min, serum bilirubin, and AST (SGOT); eosinophilia;hypokalemia.Human drug drug interactions: Dapsone may inhibitthe anti-inflammatory activity of Lamprene [FDA la-bel].Human potential toxicity: Gastrointestinal toxicity:Abdominal pain, diarrhoea, nausea, vomiting orgastrointestinal intolerance occur in 40 50% ofpatients on Lamprene. There are reports of deathfollowing severe abdominal symptoms. Autopsieshave revealed crystalline deposits of CLOF invarious tissues including the intestinal mucosa, liver,spleen, and mesenteric lymph nodes. Ames testreveals no evidence of carcinogenicity risk but long-term studies are incomplete (Reddy et al.8 andFDA label).It has been found that Lamprene crosses the humanplacenta. The skin of infants born to women whohad received the drug during pregnancy was foundto be deeply pigmented at birth. No evidence of

teratogenicity was found in these infants. There areno adequate and well-controlled studies in pregnantwomen. Lamprene should be used during pregnancyonly if the potential benefit justifies the risk to thefoetus [FDA label].Human adverse reactions: Gastrointestinal toxicity:abdominal and epigastric pain, diarrhoea, nausea,vomiting, gastrointestinal intolerance (40 50%).Reddish black reversible skin discoloration may takeseveral months or years to disappear after theconclusion of therapy. Eye pigmentation may arisedue to CLOF crystal deposits, also general eyeirritation. Discoloration of urine, faeces, sputum,sweat; elevated blood sugar; elevated erythrocytesedimentation rate [FDA label].CNS: Headache, dizziness, drowsiness, fatigue andtaste disorder. Some patients developed depressionbecause of the skin discoloration.Skin: Pigmentation from pink to brownish-black in75 100% of the patients within a few weeks oftreatment; ichthyosis and dryness (8 28%); rash andpruritus (1 5%).Depression secondary to skin discoloration; twosuicides have been reported.

References1. Reddy V, et al. (1996) Antituberculosis activities of

clofazimine and its new analogs B4154 and B4157.Antimicrob Agents Chemother 40, 633 6.

2. Fortun J, et al. (2005) Linezolid for the treatment ofmultidrug-resistant tuberculosis. J Antimicrob Chemother56, 180 5.

3. Oliva B, et al. (2004) Anti-staphylococcal activity and MOAof clofazamine. J Antimicrob Chemother 53, 435 40.

4. Steele H, et al. (1999) Inhibition of potassium transportand growth of mycobacteria exposed to clofazimine andB669 is associated with a calcium-independent increasein microbial phospholipase A2 activity. J AntimicrobChemother 44, 209 16.

5. Cholo M, et al. (2006) Effects of clofazimine on potassiumuptake by a Trk-deletion mutant of Mycobacteriumtuberculosis. J Antimicrob Chemother 57, 79 84.

6. van Rensburg C, et al. (1992) Antimicrobial activities ofclofazamine and B669 are mediated by lysophospholipids.Antimicrob Agents Chemother 36, 2729 35.

7. Barry V, et al. (1957) A new series of phenazines (rimino-compounds) with high antituberculosis activity. NatureLondon 179, 1013 5].

8. Reddy V, et al. (1999) Antimycobacterial activities ofriminophenazines. J Antimicrob Chemother 43, 615 23.

9. Boshoff H, et al. (2004) The transcriptional responses ofMycobacterium tuberculosis to inhibitors of metabolism:novel insights into drug mechanisms of action. J Biol Chem279, 40174 84.


CLOF

Clofazimine 99

11. De Logu A, et al. (2002) Activity of a new class of iso-nicotinoylhydrazones used alone and in combination withisoniazid, rifampicin, ethambutol, para-aminosalicylicacid and clofazimine against Mycobacterium tuberculosis.J Antimicrob Chemother 49, 275 82.

12. Bulatovic V, et al. (2002) Oxidative stress increasessusceptibility of Mycobacterium tuberculosis to isoniazid.Antimicrob Agents Chemother 46, 2765 71.

13. Adams L, et al. (1999) Effective treatment of acute andchronic murine tuberculosis with liposome-encapsulatedclofazimine. Antimicrob Agents Chemother 43, 1638 43.

14. Mehta R (1996) Liposome encapsulation of clofaziminereduces toxicity in vitro and in vivo and improvestherapeutic efficacy in the beige mouse model ofdisseminated Mycobacterium avium M. intracellularecomplex infection. Antimicrob Agents Chemother 40,1893 902.

15. Peters K, et al. (2000) Preparation of a clofaziminenanosuspension for intravenous use and evaluation ofits therapeutic efficacy in murine Mycobacterium aviuminfection. J Antimicrob Chemother 45, 77 83.

16. Gangadharam P, Reddy M (1995) Carryover of clofazimineinto culture media. Antimicrob Agents Chemother 39,1388 9.

17. Mukherjee J, et al. (2004) Programmes and principles intreatment of multidrug-resistant tuberculosis. Lancet 363,474 81].

18. du Toit L, et al. (2006) Tuberculosis chemotherapy: currentdrug delivery approaches. Respir Res 7, 118.

19. Sansarricq H (editor, 2004). Multidrug therapy againstleprosy: development and implementation over the past25 years. Geneva: WHO. ISBN 92 4 159176 5.

20. Nix D, et al. (2004) Pharmacokinetics and relativebioavailability of clofazimine in relation to food, orangejuice and antacid. Tuberculosis 84, 365 73.

21. Mamidi N, et al. (1995) Tissue distribution and depositionof clofazimine in rat following subchronic treatmentwith or without rifampicin. Arzneimittelforschung 45,1029 31.

22. Peters K, et al. (2000) Preparation of a clofaziminenanosuspension for intravenous use and evaluation ofits therapeutic efficacy in murine Mycobacterium aviuminfection. J Antimicrob Chemother 45, 77 83.

23. Das R, Roy B (1990) Evaluation of genotoxicity of clofaz-imine, an antileprosy drug, in mice in vivo. I. Chromosomeanalysis in bone marrow and spermatocytes. Mutat Res241, 161 8.

24. Roy B, Das R (1990) Evaluation of genotoxicity ofclofazimine, an antileprosy drug, in mice in vivo.II. Micronucleus test in bone marrow and hepatocytes.Mutat Res 241, 169 73.

Tuberculosis (2008) 88(2) 100–101

CycloserineGeneric and additional names: d-4-Amino-3-isoxazolidone; orientomycinCAS name: d-4-Amino-3-isoxazolidinoneCAS registry #: 68-41-7Molecular formula: C3H6N2O2Molecular weight: 102.09Intellectual property rights: Generic, marketed 1952

NHO

OH2N

Brand names: Closina; Farmiserina (Farmitalia); Micoserina; Oxamycin (Merck & Co.); Seromycin (Lilly)Solubility: Soluble in water, slightly soluble in methanol, propylene glycol. Forms salts with acids and bases

[Merck Index].Polarity: Log P 1.631 [DrugBank]Acidity/basicity: Aqueous solutions have a pH around 6 [Merck Index]Stability: Neutral or acid solutions are unstable. Aqueous solutions buffered to pH 10 with sodium carbonate

can be stored without loss for one week at +4ºC [Merck Index].Melting point: 147ºC [DrugBank]Formulation and optimal human dosage: 250 mg tablet, dose is 500 750 mg daily1

Basic biology informationDrug target/mechanism: Cycloserine (CYS) is an ana-log of the amino acid d-alanine. CYS inhibits alanineracemase (Alr, converts l-alanine to d-alanine) andd-alanine:d-alanine ligase (Ddl) which synthesizesthe pentapeptide core using d-alanine; both enzymesare essential in the synthesis of peptidoglycan andsubsequently in cell-wall biosynthesis and mainte-nance.1 In Mycobacterium smegmatis inactivation ofAlr or Ddl resulted in increased sensitivity to CYSwhile overexpression of Alr resulted in resistance (re-viewed in Zhang 20052). Alr appears to be the majortarget in M. smegmatis. The precise target of CYS hasnot yet been demonstrated using genetic manipula-tion in M. tuberculosis (reviewed in Zhang 20052).Drug resistance mechanism: In a 1999 Italian study10% of the M. tuberculosis clinical isolates examinedwere resistant to CYS.3 In a very large study fromTaiwan 693 M. tuberculosis strains were examinedand the overall resistance rates for individual drugswere assessed; rates for CYS were 81.8% resistantin 1996 and 51.6% resistant in 2000, however theactual rates for this study have not been validated.4

In a third study, M. tuberculosis CYS resistance rateswere 7.4%.5 Although the precise mutation has notbeen identified in M. tuberculosis, in M. smegmatisoverexpression of the alanine racemase gene isnecessary and sufficient to confer resistance.6

In-vitro potency against MTB: MIC M. tuberculosis(H37Rv): 25mg/ml.7

Spectrum of activity: CYS is a broad-spectrumantibiotic. It is most often used in combination withup to 5 drugs to treat M. avium complex (MAC) andtuberculosis [DrugBank]. CYS may be bactericidalor bacteristatic, depending on local concentrationeffects as well as efficacy against the particularstrain involved [DrugBank].Other in-vitro activity: CYS (50mg/ml) resulted inkilling <1 log (80%) of the initial innoculum whentested against M. tuberculosis in macrophages.7 CYSshowed synergistic activity with an experimentaldrug b-chloro-d-alanine which reduced the MICfrom 50 to 2.5mg/ml.8 An experimental surfactantCRL8131 had a synergistic effect when tested againstM. tuberculosis-infected macrophages with CYS.9

In-vivo efficacy in animal model: CYS (300 mg/kg)was administered 5× weekly to mice for 30 days withdrug beginning 1 day after infection. Lung CFUs werenot significantly reduced and spleen CFUs reducedfrom log 5.57 to log 5.26. CYS is known to have a highexcretion rate in mice (reviewed in Fattorini et al.200310).

Efficacy in humansCYS is a bacteristatic agent; when used to treattuberculosis, it is administered orally as 250 mg doses


CYS

Cycloserine 101

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Human 10 25 30* - - *Cmax after a dose of 250 mg every12 hours [DrugBank]

2 3 times daily.1 It is an effective agent but severetoxicity has limited its use.1 CYS rapidly and almostcompletely absorbed (70 90%) from the gut followingoral administration [DrugBank].

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Human: Half-life is longer in renally impaired

patients [DrugBank].Human metabolic pathway: Excretion is primarilyrenal, with 50% excreted unchanged within 12 hours,70% excreted within 24 hours. Widely distributed tomost body fluids and tissues, including CSF, breastmilk, bile, sputum, lymph tissue, lungs, and ascitic,pleural, and synovial fluids, CYS crosses the placenta[DrugBank].

Safety and TolerabilityAnimal toxicity: Oral LD50 in mouse is 5290 mg/kg,and in rat is over 5000 mg/kg [DrugBank].Animal safety pharmacology: CNS: Convulsions wereinduced in chicks with CYS but coadministration ofpyridoxine reversed the effects.Human drug drug interactions: CYS may interferewith the PK and absorption of isoniazid (INH) andthionamide [DrugBank]. It should be used with carein alcoholics (increased risk of seizures), patientswith a history of mental illness (CYS may increaseanxiety and depression) and patients with a historyof seizures [DrugBank].Human potential toxicity: CNS toxicity is common:dose-related neuropsychiatric effects, drowsiness,slurred speech;1 up to 50% of patients on 1 gdrug/day exhibit some of these symptoms which arereduced as the dose drops to 250 mg 2 3 times/day.1

CYS should not be given to patients with renalimpairment where a creatinine clearance of <50 mlper minute is observed. Administration of 200

300 mg of pyridoxine daily may help to prevent CYS-related neurotoxicity [DrugBank].Human adverse reactions: Symptoms of CYS over-dose are generally neuropsychiatric and includeconvulsions, seizures, slurred speech, paralysis andunconsciousness [DrugBank].

References


2. Zhang Y (2005) The magic bullets and tuberculosis drugtargets. Annu Rev Pharmacol Toxicol 45, 529 64.

3. Fattorini L, et al. (1999) Activity of 16 antimicrobialagents against drug-resistant strains of Mycobacteriumtuberculosis. Microb Drug Resist 5, 265 70.

4. Lu P, et al. (2003) The decline of high drug resistancerate of pulmonary Mycobacterium tuberculosis isolatesfrom a southern Taiwan medical centre, 1996 2000. Int JAntimicrob Agents 21, 239 43.

5. Balabanova Y, et al. (2005) Multidrug-resistant tuberculo-sis in Russia: clinical characteristics, analysis of second-line drug resistance and development of standardizedtherapy. Eur J Clin Microbiol Infect Dis 24, 136 9.

6. Ramaswamy S, et al. (1998) Molecular genetic basisof antimicrobial agent resistance in Mycobacteriumtuberculosis: 1998 update. Tubercl Lung Dis 79, 3 29.


8. David S (2001) Synergic activity of d-cycloserine andb-chloro-d-alanine against Mycobacterium tuberculosis.J Antimicrob Chemother 47, 203 6.

9. Jagannath C, et al. (1995) Activities of poloxamer CRL8131against Mycobacterium tuberculosis in vitro and in vivo.Antimicrob Agents Chemother 39, 1349 54.

10. Fattorini L, et al. (2003) Activities of moxifloxacin aloneand in combination with other antimicrobial agents againstmultidrug-resistant Mycobacterium tuberculosis infectionin BALB/c mice. Antimicrob Agents Chemother 47, 360 2.

Tuberculosis (2008) 88(2) 102–105

EthambutolGeneric and additional names: Ethambutol; (+)-2,2′-(ethylenediimino)di-1-

butanol; d-N,N′-bis(1-hydroxymethylpropyl)ethylenediamine; EMBCAS name: 2,2′-(1,2-Ethanediyldiimino)bis-1-butanolCAS registry #: 74-55-5Molecular formula: C10H24N2O2Molecular weight: 204.31Intellectual property rights: Generic, first used in TB treatment in 1966

MeN

H

HN

Me

OH

OH

Brand names: Aethambutolum, D-Ethambutol, Dadibutol, Diambutol, EMB,Ethambutol HCL, Etibi, Myambutol, Tibutol

Solubility: Dihydrochloride: Soluble in water, DMSO; sparingly soluble in ethanol; difficult to dissolve in acetoneand chloroform [Merck Index]

Polarity: Log P 0.14 [DrugBank]Acidity/basicity: ETH HCl has two apparent dissociation constants, pKa1 = 6.35, pKa2 = 9.35. In solution at

neutrality the monohydrochloride predominates1

Melting point: ETH, 88ºC; ETH HCl, 200ºC [Merck Index]Formulation and optimal human dosage: Available as 100 and 400 mg tablets. 15 mg/kg daily or up to 25 mg/kg

but risk of ocular toxicity. Weekly dose, 30 mg/kg 3 times/week [FDA label].

Basic biology informationDrug target/mechanism: Ethambutol (ETH) inhibitsarabinosyl transferases involved in cell-wall biosyn-thesis; in Mycobacterium smegmatis two polymersseem to be directly affected, arabinogalactan (AG)and lipoarabinomannan (LAM). AG forms part ofthe mucolyl-AG-peptidoglycan layer which anchorsthe peptidoglycan layer to the lipid-mycolic acidouter layer. LAM appears to be attached tothe cell membrane via phosphatidyl-inositol.2 InM. smegmatis, ETH inhibited synthesis of arabinancompletely and inhibited AG synthesis most likely asa consequence of this; more than 50% of the cellarabinan was released from the bacteria followingETH treatment, whereas no galactan was released.2

Multiple arabinosyl transferase enzymes exist but theembB gene product seems to be the main targetin M. avium,3 and in a study of M. tuberculosisresistant mutants 60% had changes in the embBgene.4 However knock-outs in M. smegmatis ofembA, embB and embC were all viable; embB wasthe slowest growing.5 embA and embB appear tobe involved in the synthesis of AG whereas embC isassociated with LAM synthesis.6

Drug resistance mechanism: Mutations in M. tu-berculosis embA or embB resulted in MICs of

10 50mg/ml although embB mutations may be morecommon.3 One of the most common mutationsin M. tuberculosis is Met306 in embB, which isoften replaced by isoleucine, leucine or valine.4

Resistance can be transferred through expressionof M. tuberculosis ETH-resistant embB gene in awild-type recipient (reviewed in Ramaswamy et al.20004). Mutants in multiple emb genes may haveeven higher MICs. ETH mutants (~25% in somestudies) with no changes in the emb genes havealso been identified.4 Stepwise mutations appear tooccur, no cross-resistance with other TB agents hasbeen observed [FDA label].In-vitro potency against MTB: MIC M. tuberculosis(H37Rv): 0.5mg/ml.7

Spectrum of activity: ETH is effective againstactively growing microorganisms of the genusMycobacterium, including M. tuberculosis. Nearly allstrains of M. tuberculosis and M. kansasii as well asa number of strains of the M. avium complex (MAC)are sensitive to ETH.8

Other in-vitro activity: When M. tuberculosis-infected macrophages were treated with ETH,the log CFUs following treatment for 3 dayswere as follows: 3mg/ml = 4.32; 6mg/ml = 4.17;control value = 4.8. The MICs for M. avium (MTCC


ETH

Ethambutol 103

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Mouse - - 3.5* - - *Cmax in mice orally dosed with16 mg/kg14

Human 2.6 24.9 5.0 467 ml/min Prospective study PK evaluatedafter 2 months daily treatment with100+ patients, dose median value24.5 mg/kg.15 FDA label onmyambutol: Cmax 2 5mg/ml (2 4 hafter dosing), drug undetectable24 hours after last dose except incases of renal insufficiency.

1723) and M. smegmatis (MTCC 6) were 15mg/ml and0.18mg/ml, respectively.9

In-vivo efficacy in animal model: In vivo in mouse(drug given orally 15 days post i.v. infection 1×/weekfor 5 weeks) log CFU reductions: untreated, 5.07;100 mg/kg, 4.59.9 In a mouse efficacy study ETH wasdosed for 12 weeks with isoniazid (INH) or alternatedays with rifampin (RIF) and pyrazinamide (PZA);CFUs in this study group were significantly lowerthan ETH, PZA, INH and RIF dosed together 3 timesweekly.10 The complexity of the experimentalconditions and observations in this work using only 4drugs serves to illustrate the difficulty in optimizingthe dose for TB treatment.

Efficacy in humansETH is described as “fourth drug” for empirictreatment of M. tuberculosis and M. avium.11

ETH is used as an adjunct in the treatmentof pulmonary tuberculosis especially in cases ofsuspected drug resistance. ETH should not be usedalone due to the real risk of resistant mutants.ETH plus INH or streptomycin (STR) have bothbeen recommended [FDA label]. Treatment regimemost often used: initially INH, RIF, PZA, ETH dailyfor 2 months followed by INH and RIF 3 timesweekly for 4 months [DrugBank]. Specific dosesand specific treatment times vary and detailscan be found in many sources including Centersfor Disease Control [http://www.cdc.gov/mmwR/preview/mmwrhtml/rr5211a1.htm] and the WorldHealth Organization [http://www.who.int/en/].In a human clinical study in 100 patients ETHappeared to lack sterilizing activity and may inhibitsterilizing activities of other TB drugs at least inthe first 14 days of treatment;12 when used as theprimary drug in an intermittent regimen ETH-treatedpatients exhibited a high relapse rate (reviewed inMitchison 200413). The standard 15 mg/kg daily ismarginally effective. According to Mitchison13 ETH

has not been adequately tested for its efficacy in acombinatorial treatment regimen.

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Human: Bioavailability from oral dose is ~75 80%.

ETH levels appear to increase with age, andpatients with a history of TB exhibited lower druglevels.15 Details of ETH human PK can be found inPeloquin et al. (1999).11

• Elephant: PK of ETH gave a 1 2 hour half-life.16

Human metabolic pathway: Hepatic: Compoundis metabolized to an aldehydic intermediate,followed by conversion to a dicarboxylic acid.Mainly renal excretion, 50% excreted unchanged,8 15% as metabolites. 20 22 percent excreted inthe faeces. No drug accumulation with single dailydoses of 25 mg/kg in patients with normal kidneyfunction, marked accumulation in patients withrenal insufficiency. ETH is excreted into breast milk[FDA label].

Safety and TolerabilityAnimal drug drug interactions: No significant drugdrug interactions noted.Animal toxicity: LD50 in mice (g/kg): 2.8 orally;2.21 i.p. [Merck Index]. Oral rat LD50: 4 g/kg.In rhesus monkeys given high doses over severalmonths neurological signs were observed andthe severity of these was proportional to drugconcentrations in serum [FDA label].Reproductive toxicology: ETH is teratogenic in miceand rabbits when administered in high doses.Birth abnormalities seen in mice and rabbits givenhigh doses included cleft palate and skeletalmalformations [FDA label].When pregnant mice or rabbits were treated withhigh doses of ETH, fetal mortality was slightly but notsignificantly (P> 0.05) increased. Female rats treated

104 Ethambutol

with ETH displayed slight but insignificant (P> 0.05)decreases in fertility and litter size.In foetuses born of mice treated with high dosesof ETH during pregnancy, a low incidence of cleftpalate, exencephaly and abnormality of the verte-bral column were observed. Minor abnormalities ofthe cervical vertebra were seen in the newborn ofrats treated with high doses of ETH during pregnancy.Rabbits receiving high doses of ETH during pregnancygave birth to two foetuses with monophthalmia,one with a shortened right forearm accompaniedby bilateral wrist-joint contracture and one withhare lip and cleft palate.Animal safety pharmacology: Toxicological studies indogs on high prolonged doses produced evidence ofmyocardial damage and failure, and depigmentationof the tapetum lucidum of the eyes, the significanceof which is not known [FDA label]. Degenerativechanges in the central nervous system, apparentlynot dose-related, have also been noted in dogsreceiving ETH over a prolonged period.In the rhesus monkey, neurological signs appearedafter treatment with high doses given daily overa period of several months. These were correlatedwith specific serum levels of ETH and with definiteneuroanatomical changes in the central nervoussystem. Focal interstitial carditis was also noted inmonkeys which received ETH in high doses for aprolonged period.Human drug drug interactions: ETH interacts withantacids; it is recommended to avoid concurrentadministration of ETH with aluminium-hydroxidecontaining antacids for at least 4 hours followingETH administration as oral absorption may beinhibited; patients coadministered antacids and drugshowed a reduction of 20% in serum concentrationand 13% in urinary excretion.11

A decrease in renal excretion of ETH occurs whengiven together with RIF.17

Human potential toxicity: Optic neuropathy andoccasional hepatotoxicity are seen. Concentrationabove 10mg/ml can adversely affect vision. Thiseffect may be related to dose and durationof treatment; it is generally reversible whenadministration of the drug is discontinued promptly.In rare cases recovery may be delayed for up toone year or more. Irreversible blindness has beenreported [FDA label].Optic neuropathy including optic neuritis or retro-bulbar neuritis occurring in association with ETH ther-apy may be characterized by one or more of thefollowing events: decreased visual acuity, scotoma,color blindness, and/or visual defect. These eventshave also been reported in the absence of a diagnosisof optic or retrobulbar neuritis [FDA label].

Patients should be advised to report promptlyto their physician any change of visual acuity[DrugBank].Human adverse reactions: The most common toxiceffect of ETH is optic neuropathy, generallyreversible although irreversible blindness has beenreported. Hepatotoxicity has been reported; base-line and periodic assessment of hepatic functionshould be performed during treatment. Otherside effects that have been observed are pruritus,joint pain, gastrointestinal upset, abdominal pain,malaise, headache, dizziness, mental confusion, dis-orientation, and possible hallucinations [FDA label].Specifically in 12 human cases receiving prophylacticETH (~23 mg/kg) and PZA (~17 mg/kg) daily for amedian of 119 days, 7 of 19 had elevated liverenzymes (alanine and aspartate aminotransferases)and treatment was discontinued; the authors suggestclose monitoring of liver toxicity when these twodrugs are used together for prophylaxis.18

No differences in safety or tolerability were observedin elderly patients [FDA label].

References

1. Beggs W, Andrews F (1974) Chemical characterizationof ethambutol binding to Mycobacterium smegmatis.Antimicrob Agents Chemother 5, 234 9.

2. Deng L, et al. (1995) Recognition of multiple effectsof ethambutol on metabolism of mycobacterial cellenvelope. Antimicrob Agents Chemother 39, 694 701.

3. Belanger A, et al. (1996) The embAB genes ofMycobacterium avium encode an arabinosyl transferaseinvolved in cell-wall arabinan biosynthesis that is thetarget for the antimycobacterial drug ethambutol. ProcNatl Acad Sci USA 93, 11919 24.

4. Ramaswamy S, et al. (2000) Molecular genetic analysis ofnucleotide polymorphisms associated with ethambutol re-sistance in human isolates of Mycobacterium tuberculosis.Antimicrob Agents Chemother 44, 326 36.

5. Escuyer V, et al. (20001) The role of the embA andembB gene products in the biosynthesis of the terminalhexaarabinofuranosyl motif of Mycobacterium smegmatisarabinogalactan. J Biol Chem 276, 48854 62.

6. Berg S, et al. (2005) Roles of conserved proline andglycosyltransferase motifs of EmbC in biosynthesis of oflipoarabinomannan. J Biol Chem 280, 5651 63.


8. Chan E, et al. (2003) Pyrazinamide, ethambutol,ethionamide, and aminoglycosides. In: Rom WN, Garay SM(editors), Tuberculosis, 2nd edition. Philadelphia, PA:Lippincott Williams & Wilkins, pp. 773 789.

9. Kaur D, Khuller G (2001) In vitro, ex-vivo and in vivoactivities of ethambutol and sparfloxacin alone andin combination against mycobacteria. Int J AntimicrobAgents 17, 51 5.

ETH

Ethambutol 105

10. Guy A, et al. (1993) Turning intermittent regimens intodaily regimens using blister-packs. An exploration inmurine tuberculosis. Tubercle Lung Dis 74, 310 6.

11. Peloquin C, et al. (1999) Pharmacokinetics of ethambutolunder fasting conditions, with food, and with antacids.Antimicrob Agents Chemother 43, 568 72.

12. Jindani A, et al. (2002) Bactericidal and sterilizingactivities of antituberculosis drugs during the first 14 days.Am J Respir Crit Care Med 167, 1348 54.

13. Mitchison D (2004) Antimicrobial therapy of tuberculosis:justification for currently recommended treatmentregimens. Semin Respir Crit Care Med 25, 307 315].

14. Pandey R, et al. (2006) Chemotherapeutic efficacy ofnanoparticle encapsulated antitubercular drugs. DrugDelivery 13, 287 94.

15. McIlleron H, et al. (2006) Determinants of rifampin, iso-niazid, pyrazinamide, and ethambutol pharmacokineticsin a cohort of tuberculosis patients. Antimicrob AgentsChemother 50, 1170 7.

16. Maslow J, et al. (2005) Pharmacokinetics of ethambutol(EMB) in elephants. J Vet Pharmacol Ther 28, 321 3.

17. Breda M, et al. (1999) Effect of rifabutin on ethambutolpharmacokinetics in healthy volunteers. Pharmacol Res40, 351 6.

18. Younossian A, et al. (2005) High hepatotoxicity ofpyrazinamide and ethambutol for treatment of latenttuberculosis. Eur Respir J 26, 462 4.

Tuberculosis (2008) 88(2) 106–108

EthionamideGeneric and additional names: EthionamideCAS name: 2-Ethyl-4-pyridinecarbothioamideCAS registry #: 536-33-4Molecular formula: C8H10N2SMolecular weight: 166.24Intellectual property rights: Generic

N

NH2S

Me

Brand names: Trecator (Wyeth); Nisotin; Trescatyl (M&B); Aetina; Ethimide; Iridocin (Bayer); Tio-MidDerivatives: Prothionamide is the propyl analog of ethionamideSolubility: Very sparingly soluble in water, ether. Sparingly soluble in methanol, ethanol, propylene glycol.

Soluble in hot acetone, dichloroethane. Freely soluble in pyridine [Merck Index].Polarity: Log P 0.705 [DrugBank]Melting point: 163ºC [DrugBank]Formulation and optimal human dosage: Supplied in 250 mg tablets, recommended dose 750 mg orally

[FDA label]Therapy is usually initiated at 250 mg daily, with gradual titration to optimal doses as tolerated by thepatient. A regimen of 250 mg daily for 1 or 2 days, followed by 250 mg twice daily for 1 or 2 days with asubsequent increase to 1 g in 3 or 4 divided doses has been reported [FDA label].

Basic biology informationDrug target/mechanism: Mode of action of theactivated form of ethionamide (ETA) is via inhibitionof the inhA gene product enoyl-ACP reductase.1,2

The wild-type (WT) inhA gene from Mycobacteriumtuberculosis conferred resistance to isoniazid (INH)and ETA when it was overexpressed in M. smegmatisand M. bovis.1 In this regard its mechanism ofaction is thought to be identical to INH althoughthe pathway of activation is distinct from thatof INH. ETA is activated by a katG-independentmechanism leading to the formation of an S-oxidemetabolite that has considerably more activitythan the parent drug (reviewed in Baulard et al.20003). In a series of papers describing experimentsin M. tuberculosis, M. bovis and M. smegmatis,ethA (also called etaA), which codes for a flavinmono-oxygenase, is reported to be responsible foractivation of ETA; expression of this gene is in partcontrolled by ethR (also called etaR), a transcrip-tional repressor gene.3 5 M. tuberculosis mutantsoverexpressing EtaA were hypersensitive to drugwhile EtaR over-expressors were drug resistant.5

The active forms of ETA and prothionamide (PRO)have been crystallized with M. tuberculosis andM. leprae InhA.6

Drug resistance mechanism: Due to the distinct acti-vation mechanisms between INH and ETA, clinicallyderived M. tuberculosis ETA mutants, often cross-resistant with thiacetazone or thiocarlide, are notcross-resistant with INH. This apparent discrepancyarises because many naturally occurring ETA mutantsharbor changes in the enzymes responsible fordrug activation.3 Laboratory-derived mutants in thetarget gene inhA do show cross-resistance betweenINH and ETA. There is complete cross-resistancebetween PRO and ETA.7 Thiocarlide and thiacetazoneare likely activated by EthA but have a distinct modeof action.6

In-vitro potency against MTB: MIC M. tuberculosis(H37Rv): 0.25mg/ml.8

Spectrum of activity: ETA has activity againstM. tuberculosis, M. bovis and M. smegmatis.3 ETAalso has activity against M. leprae (reviewed inFajardo et al. 20069 and Wang et al. 20076).Other in-vitro activity: ETA and PRO are bactericidal.MIC against M. tuberculosis H37Rv in macrophages is6.25 12.5mg/ml.10

In-vivo efficacy in animal model: ETA was lessactive than the equivalent dose of INH in a mousemodel of tuberculosis: ETA had activity against WTM. tuberculosis in a mouse model when drug was


ETA

Ethionamide 107

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Human 1.92 7.67 2.16 93.5 L(sugar-coatedtablet)

Mean PK for 250 mg oral dose usingfilm-coated tablet in healthy adults[FDA label].

administered one week after infection and continuedat 5 doses/week for 4 weeks; the log CFUs/lung forcontrol, ETA 25 mg/kg, ETA 50 mg/kg, ETA 75 mg/kgand INH 25 mg/kg were 8.01, 6.67, 6.79, 6.58, and5.59 respectively.11 Using a clinical isolate of M. tu-berculosis resistant to rifampin (RIF) (MIC 64mg/ml),pyrazinamide (PZA) (MIC > 256mg/ml) and INH (MIC1mg/ml), but sensitive to ETA (MIC 2mg/ml againstresistant strain compared with 4mg/ml againstH37Rv), ETA demonstrated activity in a mouse model(compound given by oral gavage 5 times a week for4 weeks) of M. tuberculosis with a log reductionof 2.96 and 0.43 in lung CFUs using 125 mg/kgand 50 mg/kg, respectively. INH worked better thanexpected against this strain in the mouse with alog reduction in lung CFUs of 1.65 and 2.19 at25 mg/kg and 75 mg/kg, respectively. RIF and PZAwere inactive or very weakly active.12

Efficacy in humansIn second-line therapy for drug-resistant TB, ETAshould be administered with other agents due torapid resistance development when the drug isused as monotherapy. Use of the drugs ETA andPRO is increasing in light of MDR-TB.6 ETA is usedinterchangeably with PRO.6

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Human: PK parameters differed between healthy

subjects and TB patients, resulting in a lowerAUC for TB patients, possibly due to decreasein bioavailability.13 A 500 mg dose appears tobe the minimum required to achieve serumconcentrations above the MIC.13 There is littleeffect of food or antacids on the PK of ETA;the drug can be administered with food if drugtolerance is an issue.14

Human metabolic pathway: ETA is widely distributedthroughout body tissues and fluids. Extensivemetabolism occurs mostly in the liver; ETA is me-tabolized to the M. tuberculosis active metabolitesulfoxide, and several inactive metabolites. Lessthan 1% of a dose appears in the urine as unchanged

drug, the remainder is excreted in the urine asinactive metabolites [FDA label].

Safety and TolerabilityAnimal toxicity: Teratogenic potential in rabbits andrats.Human drug drug interactions: ETA can potentiatethe effects of other TB drugs and may increaselevels of INH and cycloserine (CYS). Excess ethanoluse in combination with ETA can lead to psychoticreactions. Contraindicated in hepatitis patients[FDA label].Human potential toxicity: Blood glucose levelsrequire monitoring during treatment [FDA label].Gastrointestinal: most common side effects arenausea, vomiting, diarrhoea, abdominal pain, exces-sive salivation, metallic taste, stomatitis, anorexiaand weight loss. The effect is dose related withapproximately 50% of patients unable to tolerate1 g as a single dose [FDA label].Hepatotoxic effects are common and occur at a fairlyhigh rate although they tend to be less serious thanwith the related drug PRO.7 Hepatic effects aredescribed as transient [FDA label], but as describedby Chan15 may continue even after the drug isdiscontinued.Other side effects: hypothyroidism, peripheral neu-ropathy and other CNS conditions including blurredvision and headaches.15,16

Human adverse reactions: Most common side effectswere gastric, with nausea and vomiting [FDA label].

References

1. Banerjee A, et al. (1994) inhA, a gene encoding a target forisoniazid and ethionamide in Mycobacterium tuberculosis.Science 263, 227 30.

2. Johnsson K, et al. (1995) Studies on the mechanism ofaction of isoniazid and ethionamide in the chemotherapyof tuberculosis. J Am Chem Soc 117, 5009 10.

3. Baulard A, et al. (2000) Activation of the pro-drugethionamide is regulated in mycobacteria. J Biol Chem275, 28326 31.

4. Engohang-Ndong J, et al. (2004) EthR, a repressor of theTetR/CamR family implicated in ethionamide resistance inmycobacteria, octamerizes cooperatively on its operator.Mol Microbiol 51, 175 88.

108 Ethionamide

5. DeBarber A, et al. (2000) Ethionamide activationand sensitivity in multidrug-resistant Mycobacteriumtuberculosis. Proc Natl Acad Sci USA 97, 9677 82.

6. Wang F, et al. (2007) Mechanism of thioamide drug actionagainst tuberculosis and leprosy. J Exp Med 204, 73 8.



9. Fajardo T, et al. (2006) A clinical trial of ethionamide andprothionamide for treatment of lepromatous leprosy. AmJ Trop Med Hyg 74, 457 61.

10. Jagannath C, et al. (1995) Activities of poloxamer CRL8131against Mycobacterium tuberculosis in vitro and in vivo.Antimicrob Agents Chemother 39, 1349 54.

11. Cynamon M, Sklaney M (2003) Gatifloxacin andethionamide as the foundation for therapy of tuberculosis.Antimicrob Agents Chemother 47, 2442 4.

12. Klemens S, et al. (1993) Therapy of multidrug-resistanttuberculosis: lessons from studies with mice. AntimicrobAgents Chemother 37, 2344 7.

13. Zhu M, et al. (2002) Population pharmacokinetics ofethionamide in patients with tuberculosis. Tuberculosis82, 91 6.

14. Auclair B, et al. (2001) Pharmacokinetics of ethionamideadministered under fasting conditions or with orangejuice, food, or antacids. Antimicrob Agents Chemother45, 810 4.

15. Chan E, et al. (2003) Pyrazinamide, ethambutol,ethionamide, and aminoglycosides. In: Rom WN, Garay SM(editors), Tuberculosis, 2nd edition. Philadelphia, PA:Lippincott Williams & Wilkins. See pp. 780 781.

16. Drucker D, et al. (1984) Ethionamide-induced goitroushypothyroidism. Ann Intern Med 100, 837 9.

GATI

Tuberculosis (2008) 88(2) 109–111

GatifloxacinGeneric and additional names: GatifloxacinCAS name: 1-Cyclopropyl-6-fluoro-1,4-dihydro-8-methoxy-7-

(3-methyl-1-piperazinyl)-4-oxo-3-quinolinecarboxylic acidCAS registry #: 112811-59-3Molecular formula: C19H22FN3O4Molecular weight: 375.39Intellectual property rights: Kyorin Pharmaceutical Co.

N

CO2H

O

N

OMe

F

HN

Me

Brand names: Tequin (Bristol-Myers Squibb); Zymar (Allergan)Derivatives: Gatifloxacin is a quinolone/fluoroquinolone antibiotic related to ciprofloxacin, enoxacin,

fleroxacin, gemifloxacin, grepafloxacin, levofloxacin, lomefloxacin, moxifloxacin, norfloxacin, ofloxacin,pefloxacin, prulifloxacin, rufloxacin, sparfloxacin, temafloxacin, trovafloxacin and sitafloxacin

Solubility: 60 mg/ml at pH 4 [DrugBank]Polarity: Log P 1.81 [DrugBank]Melting point: 182 185ºC [DrugBank]Formulation and optimal human dosage: 400 mg tablets, dose is 400 mg daily

Basic biology informationDrug target/mechanism: Gatifloxacin (GATI) is a C8-methoxy fluoroquinolone (see moxifloxacin [MOXI] fordetails on mechanism of action).Drug resistance mechanism: MOXI and GATI wereboth found to have mutant prevention concen-trations below the Cmax, GATI MPC/Cmax = 0.41.1

The C8 methoxy appears to make GATI effectiveagainst some other quinolone-resistant MTB isolates(reviewed in Dong et al. 20001).Also see MOXI.In-vitro potency against MTB: MIC M. tuberculo-sis (H37Rv): 0.25mg/ml;2 others have determinedGATI MIC to be lower at 0.03mg/ml, and MOXI MIC0.037mg/ml1.M. tuberculosis clinical isolates (23 strains): MICrange 0.007 0.12mg/ml.3

Spectrum of activity: See MOXI.Other in-vitro activity: MIC99 against M. tuberculosisis 0.03mg/ml;4 M. tuberculosis MPC is 1.5mg/ml.1

GATI performed better than ofloxacin, levofloxacin(LEV) and ciprofloxacin but equal to MOXI against100-day-old cultures of M. tuberculosis and againstthese same cultures following treatment with100 mg/ml rifampin (RIF).5

In-vivo efficacy in animal model: In animal modelsof tuberculosis GATI, MOXI and sparfloxacin arethe most active of the fluoroquinolone compounds

although in general the class is not known for itssuperior TB activity in mice, however combinationsof MOXI and GATI with isoniazid (INH) and RIF werevery promising.4

Efficacy in humansGATI was compared with other fluoquinolonesin an EBA study, where monotherapy of GATI(400 mg), MOXI (400 mg), LEV (1000 mg) or INH(300 mg) was administered daily for seven days. Thefluoroquinolones exhibit early bactericidal activity(EBA) from days 0 2 slightly less than that found withINH but greater extended EBA (days 2 7) comparedwith INH.6 GATI performed almost as well as MOXI atboth early and extended time points.6

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Human: Protein binding 20%, 96% bioavaliable.

Level in tissues is often higher than in serum, ratiosaliva:serum is 0.9:1. Often found in high levels inlung parenchyma [FDA label].

Human metabolic pathway: GATI is primarily ex-creted unchanged through the kidney, with >70%recovered from urine unchanged within 48 hours ofdosing. GATI undergoes limited biotransformation inhumans with less than 1% of the dose excreted in


110 Gatifloxacin

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Human 7.8±1.3 33.0±6.2 3.8±1.0 2.0±0.3 151±46 ml/min Dose 400 mg orally (see table inDrlica et al. 2003;4 see also Johnsonet al. 20066).

the urine as ethylenediamine and methylethylene-diamine metabolites. GATI is widely distributedthroughout the body [FDA label].

Safety and TolerabilityAnimal toxicity: No increase in neoplasms was foundin mice given GATI in the diet for 18 months atdoses up to 81 mg/kg/day in males and 90 mg/kg/dayin females; similar results were seen in rats. GATItested negative in the majority of strains in the Amestest but was positive in the TA102 strain; it was alsopositive in in vitro gene-mutation assays in Chinesehamster V-79 cells and in vitro cytogenetics assaysin Chinese hamster lung cells [FDA label].Teratogenic effect: Skeletal malformations wereobserved in the offspring of rats given 200 mg/kg/dayorally or 60 mg/kg/day intravenously during organo-genesis. GATI is slightly foetotoxic at these dosesand is not recommended for use during pregnancy[FDA label].Phototoxicity: no evidence in the hairless mouse orguinea pig models [FDA label].Animal safety pharmacology: Cardiac: GATI had noeffect on QT prolongation in the anaesthetized dogusing 10 mg/kg bolus doses [FDA label].CNS: there was no increase pro convulsant risk inmice dosed up to 100 mg/kg GATI in combination withthe NSAID Fenbufen [FDA label].Human drug drug interactions: No P450 interactionshave been observed with GATI (Fish and North 20017

and FDA label).Co-administration with multivalent cations signifi-cantly decreases GATI absorbance from the gut.7

Some quinolones have been shown to increasetheophylline serum concentrations and interferewith caffeine metabolism [DrugBank].Human potential toxicity: QTc prolongation: Fluoro-quinolones are associated with a low incidence ofcardiac toxicity; GATI is thought to have a similarrisk for cardiac toxicities as the other quinolones(reviewed in Owens and Ambrose 20058). In a risingsingle dose of 400, 800 and 1200 mg in healthyvolunteers GATI was associated with an increasein QTc interval which corresponded to GATI serumlevels [FDA label].Hepatic: GATI has been associated with severe livertoxicity and hepatic failure.9

Glucose homeostasis: the GATI product label men-tions the possibility of hypoglycaemia and this riskmay increase in the elderly (reviewed in Owens andAmbrose 20058).Arthropathies and tendonitis: Both toxicities havebeen reported for the quinolone class although LEVappears to be the quinolone associated with thehighest tendonitis rates (reviewed in Owens andAmbrose 20058).Phototoxicity: not reported for GATI (reviewed inOwens and Ambrose 20058).Human adverse reactions: GATI is generally welltolerated, with most common side effects beingCNS (dizziness, headaches) and gastrointestinal(nausea and diarrhoea). Adverse CNS-related effectswere higher with quinolones in general than withother systemic antibiotics. GATI was generallysomewhat less well tolerated than a MOXI or a LEVcomparator in terms of gastrointestinal and CNSeffects (reviewed in Owens and Ambrose 20058). Onecase of a possible GATI-related seizure has beenreported although in general GATI, MOXI and LEVare thought to lack the specific structural motifassociated with seizures (reviewed in Owens andAmbrose 20058).

References1. Dong Y, et al. (2000) Mutant prevention concentration

as a measure of antibiotic potency: studies with clinicalisolates of Mycobacterium tuberculosis. AntimicrobAgents Chemother 44, 2581 4.

2. Aubry A, et al. (2006) Novel gyrase mutations inquinolone-resistant and -hypersusceptible clinical isolatesof Mycobacterium tuberculosis: functional analysis ofmutant enzymes. Antimicrob Agents Chemother 50,104 12.

3. Alvirez-Freites E, et al. (2002) In vitro and in vivo activitiesof gatifloxacin against Mycobacterium tuberculosis.Antimicrob Agents Chemother 46, 1022 5.

4. Drlica K, et al. (2003) Fluoroquinolones as antituberculosisagents. In: Rom WN, Garay SM (editors), Tuberculosis, 2ndedition. Philadelphia, PA: Lippincott Williams & Wilkins,pp. 791 807.

5. Hu Y, et al. (2003) Sterilizing activities of fluoroquinolonesagainst rifampin-tolerant populations of Mycobacteriumtuberculosis. Antimicrob Agents Chemother 47, 653 7.

6. Johnson J, et al. (2006) Early and extended earlybactericidal activity of levofloxacin, gatifloxacin andmoxifloxacin in pulmonary tuberculosis. Int J Tuberc LungDis 10, 605 12.

GATI

Gatifloxacin 111

7. Fish D, North D (2001) Gatifloxacin, an advanced8-methoxy fluoroquinolone. Pharmacotherapy 21, 35 59.

8. Owens R, Ambrose P (2005) Antimicrobial safety: focus onfluoroquinolones. Clin Infect Dis 41(Suppl 2), S144 57.

9. Coleman C, et al. (2002) Possible gatifloxacin-inducedfulminant hepatic failure. Ann Pharmacother 36, 1162 7.

Tuberculosis (2008) 88(2) 112–116

IsoniazidGeneric and additional names: isonicotinic acid hydrazide; isonicotinoylhydrazine;

isonicotinylhydrazine; INH; rimitsid; tubazidCAS name: pyridine-4-carbohydrazideCAS registry #: 54-85-3Molecular formula: C6H7N3OMolecular weight: 137.14Intellectual property rights: Generic. First synthesized in 1912, first used clinically in 1952.

N

HN

NH2

O

Brand names: Cotinazin (Pfizer); Dinacrin (Winthrop); Ditubin (Schering); Hycozid (Takeda); Iscotin (Daiichi);Isobicina (Maggioni); Isocid (CID); Isolyn (Abbott); Isonex (Dumex); Isonizida (Bial); Isozid (Fatol); Laniazid(Lannett); Mybasan (Antigen); Neoteben (Bayer); Nicizina (Pfizer); Niconyl (Parke-Davis); Nicotibina(Lapetit); Nydrazid (Bristol-Myers Squibb); Pycazide (Smith & Nephew); Pyricidin (Nepera); Rimifon(Roche); Tibinide (Ferrosan); Tubilysin (Orion)

Derivatives: Isoniazid 4-aminosalicylateIsoniazid 4-pyridinecarboxylic acid 2-(sulfomethyl)Isoniazid methanesulfonate sodium (derivative)

Solubility: Solubility in water: ~14% at 25ºC, ~26% at 40ºC; in ethanol: ~2% at 25ºC, ~10% in boiling ethanol;in chloroform: ~0.1%. Practically insoluble in ether, benzene [Merck Index].

Polarity: Log P 0.64Acidity/basicity: pH of a 1% aqueous solution 5.5 to 6.5 [Merck Index]Melting point: 171.4ºC [DrugBank]Formulation and optimal human dosage: 5 mg/kg for adults, 10 20 mg/kg for children. Adult dosing generally

300 mg capsule administered orally, once daily; or 15 mg/kg up to 900 mg/day, two or three times/week,ideally dose administered one hour before or two hours after a meal. Concomitant administration ofpyridoxine (B6) recommended for malnourished patients, adolescents, and those predisposed to neuropathy(e.g. diabetic).Can also be given intramuscularly or intravenously [DrugBank].

Basic biology informationDrug target/mechanism: Isoniazid (INH) is a pro-drug activated by catalase-peroxidase hemoprotein,KatG. INH inhibits InhA, a nicotinamide ade-nine dinucleotide (NADH)-specific enoyl-acyl carrierprotein (ACP) reductase involved in fatty acidsynthesis. Vilcheze et al.1 reported that transferof inhA mutant gene, S94A, into wild-type (WT)Mycobacterium tuberculosis was sufficient to conferresistance to INH and ethionamide (ETA), demon-strating that this is the target for INH. Prior tothis publication some controversy had existed overthe precise mode of action of this target, in partdue to the difference in the INH susceptibility ofM. tuberculosis and M. smegmatis, and the presenceof INH conferring mutations in a number of othergenes, for example kasA.2 The role of the kasA gene

product, b-ketoacyl ACP synthase,2 and the precisenature of the INH metabolites responsible for activityremain to be determined. The crystal structures ofM. tuberculosis InhA and the related enzyme MabAare both solved.3 5

Drug resistance mechanism: Resistance mutationsoccur in the target gene (inhA) and in the activatingenzyme KatG.inhA: Specific mutations in, or overexpression of, thetarget inhA gene generate organisms with increasedMICs for INH and ethionamide (ETA), with MICsat least 5 times higher than WT.1

KatG: INH is a prodrug activated by catalase-peroxidase hemoprotein, KatG. Mutations in thekatG gene lead to high-level resistance (200× MIC)and ~50% of INH-resistant clinical isolates carry sucha mutation, often S315T.5 INH-resistant mutants with


INH

Isoniazid 113

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Mouse 1.7±0.17 52.2±2.2 28.2±3.8 Single oral dose of 25 mg/kg13

Guinea pig 3.5±0.7 10.9±1.8 1.7±0.3 Single oral dose 10 mg/kg15,16

Human FA:1.54±0.3SA: 3.68±0.59

FA: 19±6.1SA: 48.2±1.5

FA: 5.4±20SA: 7.1±1.9

Single oral dose of 6.2 mg/kg.13

FA = fast acetylators,SA = slow acetylators.

changes in the genes ahpC (alkyl hydroperoxidereductase), kasA2 and ndh (NADH dehydrogenase)have also been observed.6,7

In-vitro potency against MTB: MIC M. tuberculosis(H37Rv): 0.025mg/ml.8

Spectrum of activity: INH is a bactericidal agentactive against organisms of the genus Mycobac-terium, specifically M. tuberculosis, M. bovis andM. kansasii. INH is bactericidal to rapidly-dividingmycobacteria, but is bacteristatic if the mycobac-terium is slow-growing. INH is highly specific, beingactive against only a subset of the mycobacteria andlargely ineffective against other microorganisms;this is in part due to several unusual aspectsof metabolism, exemplified in M. tuberculosis,including unusually high KatG activity and adefective drug efflux mechanism.9

Other in-vitro activity: INH is bactericidal onlyover the first 48 hours in culture; after this theeffect is mostly bacteristatic presumably becauseall the actively growing organisms are killed rapidly,leaving the “persistors”. This reflects the effectseen in vivo with efficacy only against the fast-growing organisms.10 MICs of INH were decreased inthe presence of plumbagin and clofazimine (CLOF),both of which can generate superoxides.11 Manydrug combinations seem to synergize with INHin vitro; little additional activity was observedwhen INH alone was tested with a variety ofknown anti-TB drugs including rifampin (RIF),however significant synergy was seen when RIF andINH were tested in combination with gatifloxacin(GATI) (FIC 0.39 0.65), sparfloxacin (FIC 0.39 0.48),ciprofloxacin (FIC 0.43 0.68), clarithromycin (CLA)(FIC 0.48 0.55) and ETH (FIC 0.7 1).12 Synergy atthe MIC level was also seen with INH in combinationwith levofloxacin (LEV), with ETH and LEV, and withETH, RIF and LEV.13 INH effects on the bacteriawithin a macrophage seem somewhat controversial.Jayaram et al.10 report that INH inhibits growthof M. tuberculosis in macrophages at 0.05mg/ml,but no bactericidal activity was observed even at32mg/ml. In these experiments, despite the rapidlygrowing bacteria, bactericidal activity was notobserved. To explain this it was postulated that the

pH within the vacuole containing the bacteria wasnot conducive to drug action.10 Rastogi et al.,8 on theother hand, report that INH is active and bactericidalwhen M. tuberculosis is tested within macrophages.In-vivo efficacy in animal model: Activity in mice(dosed 14 days after infection using 6 timesweekly gavage at 25 mg/kg for 8 weeks) reducedlog CFU from 6.13 (control) to 3.47.13 Good efficacyagainst M. tuberculosis in guinea pigs, mice, andmonkeys was found at 10 mg/kg, but no increasein efficacy when the drug was administered at100 mg/kg. Bactericidal activity of INH slows downafter the first 2 3 weeks in mice, and CFUs stabilizeat a low level after 2 3 months of treatment.9

INH-resistant organisms may emerge after longertreatment with INH monotherapy.9 Labana et al.14

showed that efficacy of INH in mice could bemaintained, while reducing the therapeutic dose byone third, with the use of liposome encapsulation.

Efficacy in humansINH has high early bactericidal activity thatkills actively growing bacteria and causes rapiddecrease in sputum bacilli for the first 2 weeksof treatment, then slows down for non-growingbacterial populations (reviewed in Zhang 20039).For patients with low-level primary INH resistance(<1% bacilli resistant to 1mg/ml INH), treatmentis still suggested. Drug can be administered byoral, IV or IM routes. Treatment regime mostoften used: initially INH, RIF, PZA, ETH dailyfor 2 months followed by INH and RIF 3 timesweekly for 4 months [DrugBank]. Specific doses andspecific treatment times vary and details can befound in many sources including Centers for Dis-ease Control [http://www.cdc.gov/mmwR/preview/mmwrhtml/rr5211a1.htm] and the World HealthOrganization [http://www.who.int/en/]. INH can beused prophylactically in the case of latent disease.

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Mouse: Linear PK (oral dose) over 0.1 120 mg/kg.

In aerosol infection model AUC24/MIC is predictive

114 Isoniazid

of antimicrobial activity.10 Antagonism betweenINH, RIF and PZA is found in mice.17

• Guinea pig: Bioavailability 58%. Pandey et al.15,16

report some guinea pig PK comparing INH and RIFusing single oral dose at 12 mg/kg.

• Human: Drug concentration in lung is similar tothose in serum.9 INH levels appear to increasewith age.18 Close to 100% bioavailable under mostcircumstances.

Animal metabolic pathway: Primarily hepatic.Human metabolic pathway: Primarily hepatic. INHis acetylated to give N-acetylisoniazid, then bio-transformed to isonicotinic acid and monoacetyl-hydrazine. The rate of acetylation is geneticallydetermined (50% of blacks and whites are slowacetylators [SA], 85% of Eskimos and Asians are fastacetylators [FA]). Slow acetylators are characterizedby a relative lack of hepatic N-acetyltransferase.INH is found widely distributed in all body fluids(cerebrospinal, pleural, ascitic), tissues, organs, andexcreta (saliva, sputum, faeces); it passes throughthe placental barrier and into milk. Excretion isprimarily renal [FDA label, Jayaram et al. 200410].

Safety and TolerabilityAnimal drug drug interactions: INH (100 mg/kgdaily for 4 days by oral gavage) in rats leadsto an upregulation in CYP2E but not CYP3A. A566% increase was also seen in liver 4-nitrophenylhydroxylase activity.19

Antagonism between INH, RIF and PZA can beobserved in mice under specific circumstances eventhough these drugs are used in combination inhumans.13,17 In the initial phase of infection (first 2months) INH/RIF was as efficacious as INH/RIF/PZAbut less active than RIF/PZA. At the end ofthe continuation phase (6 months treatment) withINH/RIF or INH/RIF/PZA or RIF/PZA all animals wereapparently sterilized. After 6 months (drug free)more animals relapsed in the INH/RIF or INH/RIF/PZAgroup compared with the RIF/PZA group, suggestingantagonism between INH and RIF/PZA.17 The causeof the apparent antagonism is most likely to be theeffect of INH on the RIF AUC and Cmax, both ofwhich were decreased in the presence of INH.17 Suchantagonism may not be apparent in humans becausethe generally accepted experimental use level of INHis higher in mice compared with the standard humandose.13

Animal toxicity: Acute toxicity: LD50 in mice(mg/kg), 151 i.p., 149 i.v. [Merck Index].Reproductive toxicity: INH has embryocidal effectsin rats and rabbits when administered orally duringpregnancy, but no congenital anomalies were foundin reproduction studies in mammalian species (mice,rats and rabbits) [DrugBank].

Hepatotoxicity: INH administered in encapsulatedform once or twice a week was as effectiveas free drug and showed less liver toxicity asmeasured by ALT, alkaline phosphatase and bilirubinlevels.14,20 Favorable results were achieved with anINH-Schiff base analog to block in vivo acetylation byarylamine N-acetyltransferase (NAT). The acetylateddrug is inactive. The Schiff-base analog demon-strated an increase in mouse LD50 to ~1000 mg/kgfrom ~150 mg/kg for INH21 and may be less toxicin vivo. INH and RIF dosed simultaneously in rabbitscaused an elevation in phosholipids and a reductionin phosphatidylcholine, cardiolipin and inorganicphosphates, possibly via a choline deficiency, whichmay lead to the observed liver toxicity.22

INH has been shown to induce pulmonary tumorsin a number of mouse strains. INH has not beenshown to be carcinogenic in humans [Package Insert,Drugs.com].INH has been found to be weakly mutagenic in strainsTA 100 and TA 1535 of Salmonella typhimurium (Amesassay) without metabolic activation [Package Insert,Drugs.com].In vitro studies of a variety of animal cell linesdemonstrated that INH toxicity results from theinduction of apoptosis with associated disruption ofmitochondrial membrane potential and DNA strandbreaks.20

Animal safety pharmacology: CNS: Convulsions wereinduced in chicks with INH and a corresponding risein GABA was observed, however coadministrationof pyridoxine reversed the effects.23 INH binds topyridoxal-5-phosphate, the active form of pyridoxine(vitamin B6), to form INH-pyridoxal hydrazones.Pyridoxal-5-phosphate is a cofactor for glutamic aciddecarboxylase and GABA transaminase in the GABAsynthetic pathway. INH overdose results in decreasedpyridoxal-5-phosphate, decreased GABA synthesis,increased cerebral excitability, and seizures. Co-ingestion of ethanol potentiates toxicity by enhanc-ing degradation of phosphorylated pyridoxine. INHalso inhibits lactate dehydrogenase, an enzyme thatconverts lactate to pyruvate.Human drug drug interactions: INH interacts withthe cytochrome P450 system, especially CYP2E1,where it shows a biphasic inhibition induction; itcauses increases in serum concentrations of variousdrugs, especially phenytoin and carbamazepine,increases the effects of warfarin and theophylline,inhibits metabolism of benzodiazepines, and inhibitsmonoamine oxidase and histaminase (reviewed inSelf et al. 199924).INH should not be administered with food, asstudies have shown that this significantly reduces itsbioavailability.

INH

Isoniazid 115

Human potential toxicity: Hepatitis: Risk of de-veloping severe and sometimes fatal hepatitis isassociated with INH usage, and risk increases withage and with daily alcohol consumption. In a studyin the 1970s 10 25% of those monitored developedat least sub-clinical hepatic effects (reviewed inSanders and Sanders 197923). The drug is acetylatedin vivo and slow acetylators generally experiencehigher blood levels and a potential for increasein toxicity.25 Acetyl hydrazine is released fromacetylated INH and may be at least one of the toxiccomponents.23

CNS: Peripheral neuropathy: chronic use of INHcan produce peripheral neuropathy but this canbe prevented by the concurrent administration ofpyridoxine.Since INH is known to cross the placental barrier,neonates of INH-treated mothers should be carefullyobserved for any evidence of adverse effects.A diagnosis of mesothelioma in a child with prenatalexposure to INH and no other apparent risk factorshas been reported [Package Insert, Drugs.com].Human adverse reactions: CNS effects: Peripheralneuropathy is the most common CNS-related toxiceffect. It is dose-related, occurs most often inthe malnourished and in those predisposed toneuritis (e.g., alcoholics and diabetics), and isusually preceded by paraesthesias of the feet andhands. The incidence is higher in “slow acetylators”.Other neurotoxic effects, which are uncommonwith conventional doses, are convulsions, toxicencephalopathy, optic neuritis and atrophy, memoryimpairment and toxic psychosis [DrugBank].Hepatitis: INH does carry a specific warning ofthe potential for liver toxicity. Liver toxicity andhepatitis risks are increased with concomitantuse of carbamazepine, phenobarbital, RIF, andalcohol abuse. Elevated serum transaminase (SGOTSGPT), bilirubinaemia, bilirubinuria, jaundice, andoccasionally severe and sometimes fatal hepatitiscan occur with normal dosing regimens. The commonprodromal symptoms of hepatitis are anorexianausea, vomiting, fatigue, malaise, and weakness.Mild hepatic dysfunction, evidenced by mild andtransient elevation of serum transaminase levels,occurs in 10 20% of patients taking INH. Thisabnormality usually appears in the first 1 3 monthsof treatment but can occur at any time duringtherapy. In most instances enzyme levels returnto normal, and generally there is no necessity todiscontinue medication during the period of mildserum transaminase elevation. The frequency ofprogressive liver damage increases with age. It israre in persons under 20, but occurs in up to 2.3% ofthose over 50 years of age [Zhang 2003,9 DrugBank].

Gastrointestinal: effects such as nausea, vomiting,epigastric distress and dark urine can occur but arerare.9

Haematological effects: agranulocytosis; hemolytic,sideroblastic, or aplastic anaemia, thrombocytope-nia; and eosinophilia can occur.9

Endocrine and metabolic: pyridoxine deficiency,pellagra, hyperglycaemia, acidosis and gynecomastiacan occur.9

Hypersensitivity: fever, skin rashes, lymphadenopa-thy and vasculitis can occur.10

References

1. Vilcheze C, et al. (2006) Transfer of a point mutation inMT inhA resolves the target for isoniazid. Nat Med 12,1027 9.

2. Mdluli K, et al. (1998) Inhibition of a M. tuberculosisb-ketoacyl ACP synthase by isoniazid. Science 280,1607 10.

3. Dessen A, et al (1995) Crystal structure and function of theisoniazid target of Mycobacterium tuberculosis. Science267, 1638 41.

4. Rozwarski D, et al. (1999) Crystal structure of theMycobacterium tuberculosis enoyl-ACP reductase, InhA,in complex with NAD+ and a C16 fatty acyl substrate.J Biol Chem 274, 15582 9.

5. Cohen-Gonsaud M, et al. (2002) Crystal structure of MabAfrom Mycobacterium tuberculosis, a reductase involved inlong-chain fatty acid biosynthesis. J Mol Biol 320, 249 61.

6. Vilcheze C, et al. (2000) Inactivation of the inhA-encodedfatty acid synthase II (FASII) enoyl-acyl carrier proteinreductase induces accumulation of the FASI end productsand cell lysis of Mycobacterium smegmatis. J Bacteriol182, 4059 67.

7. Lee A, et al. (2001) Novel mutations in ndh in isoniazid-resistant Mycobacterium tuberculosis isolates. AntimicrobAgents Chemother 45, 2157 9.


9. Zhang Y (2003) Isoniazid. In: Rom WN, Garay SM (editors),Tuberculosis, 2nd edition. Philadelphia, PA: LippincottWilliams & Wilkins, pp. 739 58.

10. Jayaram R, et al. (2004) Isoniazid pharmacokineticspharmacodynamics in an aerosol infection model oftuberculosis. Antimicrob Agents Chemother 48, 2951 7.

11. Bultatovic V, et al. (2002) Oxidative stress increasessusceptibility of Mycobacterium tuberculosis to isoniazid.Antimicrob Agents Chemother 46, 2765 71.


13. Grosset J, Ji B (1998) Experimental chemotherapy ofmycobacterial diseases. In: Gangadharan P, Jenkins P(editors), Mycobacteria: II. Chemotherapy. Chapman andHall, pp. 51 97.

14. Labana S, et al. (2002) Chemotherapeutic activity againstmurine tuberculosis of once weekly administered drugs

116 Isoniazid

(isoniazid and rifampicin) encapsulated in liposomes. IntJ Antimicrob Agents 20, 301 4.

15. Pandey R, et al (2003) Poly (dl-lactide-co-glycolide)nanoparticle-based inhalable sustained drug deliverysystem for experimental tuberculosis. J AntimicrobChemother 52, 981 6.

16. Pandey R, et al. (2004) Liposome-based antituberculardrug therapy in a guinea pig model of tuberculosis. Int JAntimicrob Agents 23, 414 5.

17. Grosset J, et al. (1992) Antagonism between isoniazidand the combination pyrazinamide rifampin againsttuberculosis infection in mice. Antimicrob AgentsChemother 36, 548 51.

18. McIlleron H, et al. (2006) Determinants of rifampin, iso-niazid, pyrazinamide, and ethambutol pharmacokineticsin a cohort of tuberculosis patients. Antimicrob AgentsChemother 50, 1170 7.

19. Lake B, et al. (1998) Comparison of the effects of someCYP3A and other enzyme inducers on replicative DNAsynthesis and cytochrome P450 isoforms in rat liver.Toxicology 131, 9 20.

20. Deol P, et al. (1997) Therapeutic efficacies of isoniazid andrifampin encapsulated in lung-specific stealth liposomesagainst Mycobacterium tuberculosis infection induced inmice. Antimicrob Agents Chemother 41, 1211 4.

21. Hearn M, Cynamon M (2004) Design and synthesisof antituberculars: preparation and evaluation againstMycobacterium tuberculosis of an isoniazid Schiff base.J Antimicrob Chemother 53, 185 91.

22. Karthikeyan S (2005) Isoniazid and rifampicin treatmenton phospholipids and their subfractions in liver tissue ofrabbits. Drug Chem Toxicol 28, 273 80.

23. Sanders W, Sanders C (1979) Toxicity of antibacterialagents: mechanism of action on mammalian cells. AnnuRev Pharmacol Toxicol 19, 53 83.

24. Self T, et al. (1999) Isoniazid drug and food interactions.Am J Med Sci 317, 304 11.

25. Kinzig-Schippers M, et al. (2005) Should we use N-acetyltransferase type 2 genotyping to personalizeisoniazid doses? Antimicrob Agents Chemother 49,1733 8.

KAN

Tuberculosis (2008) 88(2) 117–118

KanamycinGeneric and additional names: -CAS name: 2-(Aminomethyl)-6-[4,6-diamino-3-[4-amino-3,5-dihydroxy-

6-(hydroxymethyl)tetrahydropyran-2-yl]oxy-2-hydroxy-cyclohexoxy]-tetrahydropyran-3,4,5-triol

CAS registry #: 8063-07-8Molecular formula: C18H36N4O11Molecular weight: 582.58Intellectual property rights: GenericBrand names: Aminodeoxykanamycin, Bekanamycin, Kanamycin A,

Kanamycin B, Kanamycin Base, Kanamycin Sulfate, Kantrex, KenamycinA, Klebcil, Nebramycin Factor 5

Derivatives: Kanamycin A, Kanamycin B, Kanamycin C

NH2

NH2HO

O

O

O

OH2N

R'

NH2

HOHO

HO

OH

R

KanamycinA: R = NH , R' = OH;

B: R = NH , R'=NH ;

C: R = OH, R' = NH .

2

2 2

2

Solubility: Kanamycin A sulfate is freely soluble in water. Practically insoluble in the common alcohols andnonpolar solvents.Kanamycin B Bekanamycin, aminodeoxykanamycin is soluble in water, formamide; slightly soluble inchloroform, isopropyl alcohol; practically insoluble in the common alcohols and nonpolar solvents.Kanamycin C is soluble in water; slightly soluble in formamide; practically insoluble in the common alcoholsand nonpolar solvents [Merck Index].

Polarity: Log P 7.936 [DrugBank]Formulation and optimal human dosage: 1 g vial, dose 1 g daily i.v. or intramuscularly (i.m.)1

Basic biology informationDrug target/mechanism: Kanamycin (KAN) is anaminoglycoside antibiotic having the same modeof action as streptomycin (STR); it inhibits proteinsynthesis by tightly binding to the conserved A siteof 16S rRNA in the 30S ribosomal subunit.1 It is in thesame class as amikacin (AMI) and STR.Drug resistance mechanism: Ribosomal changes inMycobacterium tuberculosis 16S rRNA2 lead topossible cross-resistance with other class members,STR and AMI, but this is not always complete. Forexample, KAN, AMI and capreomycin (CAP) werestill efficacious in vitro when resistance to STR haddeveloped.3 See also the Drug resistance mechanismsection for STR.In-vitro potency against MTB: MIC M. tuberculosis(H37Rv): 2mg/ml.4

Spectrum of activity: Aminoglycosides are usedmainly in infections involving aerobic, Gram-negative bacteria, such as Pseudomonas, Acineto-bacter and Enterobacter. M. tuberculosis is alsosensitive to this drug. Gram-positive bacteria canalso be treated with the drug but less toxic

alternatives tend to be utilized. Synergistic effectswith the aminoglycosides and beta lactams haveresulted in use of this combination treatmentfor streptococcal infections, especially endocarditis[DrugBank].Other in-vitro activity: KAN demonstrated goodbactericidal activity against drug-sensitive M. tuber-culosis clinical isolates, but when tested againstdrug-resistant isolates it had bactericidal activityagainst only 2 out of 5 strains when tested at8mg/ml.4

KAN had no bactericidal activity, but did causesignificant reduction in bacterial load when M. tu-berculosis-infected macrophages were treated usingaminoglycosides; there was a 1 2 log reduction inCFU, 99% killing using STR 30mg/ml or KAN 30mg/mlor AMI 20mg/ml.4

In-vivo efficacy in animal model: AMI was the mostactive of the aminoglycosides tested (STR, AMI andKAN dosed at 200 mg/kg 6 times weekly) in a mousemodel of tuberculosis (2.3×107 CFU M. tuberculosisadministered i.v. followed by dosing 1 day later).STR reduced the CFU in the spleen by almost 1 log.


118 Kanamycin

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Human 2.5 22 7.5 mg/kg dose given i.v.Intravenous administration of KANover a period of one hour resultedin serum concentrations similar tothose obtained by intramuscularadministration [DrugBank].

All three drugs were less efficacious than isoniazid(INH) at 25 mg/kg. All the mice in the drug-treatedgroups survived whereas the control mice died within30 days.5

Efficacy in humansAminoglycosides remain important drugs for treatingdiseases caused by M. tuberculosis6 but theyare no longer considered first-line agents. Theaminoglycosides and CAP cannot be administeredorally. KAN is more toxic than STR and has theweakest antibacterial activity of the aminoglycosidesin clinical use.5

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Chan et al. give a value for Cmax of 35 45mg/ml,

with no dose given.1

Human metabolic pathway: Primarily eliminatedthrough the kidney.

Safety and TolerabilityAnimal toxicity: Oral mouse LD50: 17,500 mg/kg. Oralrat LD50: >4000 mg/kg. Oral rabbit LD50: >3000 mg/kg[DrugBank].Animal safety pharmacology: Ototoxicities wereobserved in guinea pigs [FDA label].Human drug drug interactions: In vitro mixing ofan aminoglycoside with beta-lactam type antibiotics(penicillins or cephalosporins) may result in areduction in aminoglycoside serum half-life or serumlevels especially when renal function is impaired.A history of hypersensitivity or toxic reaction to one

aminoglycoside contraindicates the use of any otheraminoglycoside [DrugBank]. Also see STR and AMI.Human potential toxicity: The aminoglycosides andCAP are known for their ototoxicities, and incidencesmay be as high as 3 10%.1 Bowel lesions can increasedrug absorption [DrugBank].Human adverse reactions: KAN may lead to eighth-cranial-nerve impairment, intestinal obstruction,renal function impairment, or ulcerative lesions ofthe bowel.

References







LEV

Tuberculosis (2008) 88(2) 119–121

LevofloxacinGeneric and additional names: S-( )-form of OfloxacinCAS name: 9-fluoro-2,3-dihydro-3-methyl-10-(4-methyl-1-piperazinyl)-7-

oxo-7H-pyrido[1,2,3-de]-1,4-benzoxazine-6-carboxylic acidCAS registry #: 100986-85-4; 138199-71-0 (hemihydrate)Molecular formula: C18H20FN3O4Molecular weight: 361.37Intellectual property rights: Generic

N

CO2H

O

N

O

F

NMe Me

Brand names: Cravit (Daiichi); Levaquin (Ortho-McNeil); Tavanic (Aventis); Quixin (Santen)Derivatives: Levofloxacin is a quinolone/fluoroquinolone antibiotic related to ciprofloxacin, enoxacin,

fleroxacin, gatifloxacin, gemifloxacin, grepafloxacin, lomefloxacin, moxifloxacin, norfloxacin, ofloxacin,pefloxacin, prulifloxacin, rufloxacin, sparfloxacin, temafloxacin, trovafloxacin, sitafloxacin

Solubility: Freely soluble in glacial acetic acid, chloroform; sparingly soluble in water [Merck Index].Polarity: Log P 1.268 [DrugBank]Formulation and optimal human dosage: 500 mg tablet, dose 500 1000 mg daily

Basic biology informationDrug target/mechanism: Levofloxacin (LEV) is de-scribed as a second-generation quinolone alongwith ciprofloxacin (CIPRO) and ofloxacin (OFL). Seemoxifloxacin (MOXI) for mode of action details.Drug resistance mechanism: See MOXI.In-vitro potency against MTB: MIC Mycobacteriumtuberculosis H37Rv: 0.5mg/ml.1

Spectrum of activity: See MOXI.Other in-vitro activity: MIC99 for LEV is 0.2mg/mlagainst M. tuberculosis2 which is lower than theMIC of 0.5mg/ml obtained by Rastogi et al.1 Ingeneral most authors agree that MOXI has the lowestMIC against M. tuberculosis when comparing thiscompound to CIPRO, OFL and LEV.3 Specifically,Rodriguez et al.3 reported MICs of �2mg/ml withCIPRO for 12 strains (21.8%), with OFL for 11 strains(20%), with LEV for five strains (9%) and withMOXI for two strains (3.6%). A minimum inhibitoryconcentration of �0.5mg/ml was obtained for CIPROin 23 strains (41.8%), for OFL in 34 strains (61.8%),for LEV in 45 strains (81.8%) and for MOXI in 46strains (83.6%).3 One strain had an MIC of 128mg/mlfor CIPRO, 4mg/ml for OFL and 2mg/ml for LEVand MOXI.3 LEV performed significantly less wellthan MOXI and gatifloxin (GATI) against 100-day-old cultures of M. tuberculosis (representing thepersistent form of M. tuberculosis) and againstthese same cultures following treatment with

100mg/ml rifampin (RIF).4 LEV was active againstM. tuberculosis-infected macrophages at 0.5mg/ml(reviewed in Berning 20015).In-vivo efficacy in animal model: When LEV wastested against a mouse model of tuberculosis(107 organisms given i.v., dosing began 1 day afterinfection and continued for 28 days) INH and RIFwere superior; no differences were found betweenbetween LEV and ethambutol (ETH) or pyrazinamide(PZA) against organism load in the spleen. At equaldoses LEV was better than OFL but inferior tosparfloxacin.6 Similar results were found in a short-course (2 days) treatment regimen.7

Efficacy in humansLEV was compared with other fluoroquinolonesin an EBA study, where monotherapy of GATI(400 mg), MOXI (400 mg), LEV (1000 mg) or INH(300 mg) was administered daily for seven days. Thefluoroquinolones exhibit early bactericidal activity(EBA) from days 0 2 slightly less than that foundwith INH but greater extended EBA (days 2 7)compared with INH.8 EBA activity between the threefluoroquinolones was similar on days 2 7 but LEV wasbetter at days 0 2 compared with MOXI and GATI.8

LEV is used in combination with other drugs to treathuman tuberculosis, for example at 750 mg/daily;5

it is generally used in a second-line treatmentregimen.2


120 Levofloxacin

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Mouse 1.02 3.17mg·h/ml Single i.v. dose of 10 mg/kg to mice9

Monkey 1.86 31.79mg·h/ml 8.5 0.79 l/h/kg Single 25 mg/kg oral dose to malerhesus monkeys10

Human 7.7 8.9 71.4 110.0mg·h/ml

7 12 1.5 Dose 750 mg oral.5

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Oral bioavailability 85 95%.5

Human metabolic pathway: LEV and OFL are clearedprimarily by the kidney.5

Safety and TolerabilityAnimal drug drug interactions: In-vitro and in-vivostudies in animals indicate that LEV is neither aP450 enzyme inducer nor an inhibitor in the humantherapeutic plasma concentration range; therefore,no drug metabolizing enzyme-related interactionswith other drugs or agents are anticipated.11

Animal toxicity: Acute toxicity: The median lethaldose (LD50) values obtained in mice and ratsafter oral administration of LEV were in therange 1500 2000 mg/kg. Administration of 500 mg/kgp.o. to monkeys induced little effect apart fromvomiting.Repeated dose toxicity: Studies of one and sixmonths duration by gavage have been carried outin the rat and monkey. Doses were 50, 200,800 mg/kg/day and 20, 80, 320 mg/kg/day for 1 and6 months in the rat and 10, 30, 100 mg/kg/dayand 10, 25, 62.5 mg/kg/day for 1 and 6 months inthe monkey. Signs of reaction to treatment wereminor in the rat with slight effects principallyat 200 mg/kg/day and above in reducing foodconsumption and slightly altering haematologicaland biochemical parameters. The No ObservedAdverse Effect Level (NOAEL) in these studies wasconcluded to be 200 and 20 mg/kg/day after 1 and6 months respectively. Toxicity after oral dosingin the monkey was minimal with reduced bodyweight at 100 mg/kg/day together with salivation,diarrhoea and decreased urinary pH in someanimals at this dose. No toxicity was seen in the6-month study. The NOAELs were concluded tobe 30 and 62.5 mg/kg/day after 1 and 6 monthsrespectively.Reproductive toxicity: LEV caused no impairmentof fertility or reproductive performance in rats atoral doses as high as 360 mg/kg/day or intravenousdoses up to 100 mg/kg/day. LEV was not teratogenic

in rats at oral doses as high as 810 mg/kg/day,or at intravenous doses as high as 160 mg/kg/day.No teratogenicity was observed when rabbitswere dosed orally with up to 50 mg/kg/day orintravenously with up to 25 mg/kg/day. LEV had noeffect on fertility and its only effect on foetuseswas delayed maturation as a result of maternaltoxicity.Genotoxicity: LEV did not induce gene mutationsin bacterial or mammalian cells but did inducechromosome aberrations in Chinese hamster lungcells in vitro at or above 100mg/ml, in the absenceof metabolic activation. In-vivo tests (micronucleus,sister chromatid exchange, unscheduled DNA syn-thesis, dominant lethal tests) did not show anygenotoxic potential.Phototoxic potential: Studies in the mouse afterboth oral and intravenous dosing showed LEV tohave phototoxic activity only at very high doses.LEV did not show any genotoxic potential in aphotomutagenicity assay, and it reduced tumordevelopment in a photocarcinogenicity assay.Carcinogenic potential: No indication of carcinogenicpotential was seen in a two-year study in therat with dietary administration (0, 10, 30 and100 mg/kg/day).Toxicity to joints: In common with other fluoroquinol-ones, LEV showed effects on cartilage (blisteringand cavities) in rats and dogs. These findings weremore marked in young animals [see Levaquin productmonograph for complete toxicity listings].Animal safety pharmacology: In mice, the CNSstimulatory effect of quinolones is enhanced byconcomitant administration of non-steroidal anti-inflammatory drugs. In dogs, LEV administered at6 mg/kg or higher by rapid intravenous injectionproduced hypotensive effects. These effects wereconsidered to be related to histamine release.11

Some quinolones including LEV have been associatedwith prolongation of the QT interval and somecases of arrhythmias. LEV has a hERG IC50 of915mM, which is not as potent an inhibitor ofthe hERG channel as some other quinolones suchas Sparfloxacin (18mM), Grepafloxacin (50mM) andMOXI (129mM).12

LEV

Levofloxacin 121

Human drug drug interactions: No significant druginteractions have been observed in patients takingconcurrent treatment of LEV and theophylline,cyclosporin, digoxin, probenecid, cimetidine orzidovudine. However, disturbances in blood glucoselevels have been reported in patients taking LEV withan antidiabetic drug. Similarly, drug interactionshave been observed in patients treated with LEVand warfarin resulting in an enhancement of theanticoagulant effects of oral warfarin and itsderivatives (Product Monograph, Levaquin, Janssen-Ortho Inc).Human potential toxicity: Moderate to severephototoxicity reactions have been observed inpatients exposed to direct sunlight while receivingdrugs in this class.As with other quinolones and with LEV, disturbancesof blood glucose, including symptomatic hyper-and hypoglycaemia, have been reported, usually indiabetic patients receiving concomitant treatmentwith an oral hypoglycemic agent (e.g., glyburide/glibenclamide) or with insulin.The reports of arrhythmias generally involve patientswith either concurrent medical conditions suchas myocardial infarction or congenital QT pro-longation or those taking concurrent medications,such as amiodarone and sotalol, which prolongthe QT interval.11 Elderly patients may be moresusceptible to drug-associated effects on theQT interval. Therefore, precaution should be takenwhen using LEV with concomitant drugs thatcan result in prolongation of the QT interval(e.g. class IA or class III antiarrhythmics) orin patients with risk factors for Torsades depointes (e.g. known QT prolongation, uncorrectedhypokalemia).11

Human adverse reactions: The incidence of drug-related adverse reactions in patients during Phase 3clinical trials conducted in North America was 6.2%.Among patients receiving LEV therapy, 4.3% discon-tinued LEV therapy due to adverse experiences.Convulsions and toxic psychoses have been reportedin patients receiving quinolones, including LEV.LEV should be used with caution in patientswith a known or suspected CNS disorder thatmay predispose to seizures or lower the seizurethreshold.Peripheral neuropathies have been associated withLEV use.

The following adverse reactions can occur during LEVtreatment:

hypersensitivity reactions: skin rash, hives orother skin reactions, angioedema (e.g., swellingof the lips, tongue, face, tightness of the throat,hoarseness), or other symptoms of an allergicreaction;tendon disorders: tendonitis or tendon rupture,with the risk of serious tendon disorders beinghigher in those over 65 years of age, especiallythose on corticosteroids.phototoxicity, prolongation of the QT interval.11

References

1. Rastogi N, et al. (1996) In vitro activities of levofloxacinused alone and in combination with first- andsecond-line antituberculous drugs against Mycobacteriumtuberculosis. Antimicrob Agents Chemother 40, 1610 6.

2. Drlica K, et al. (2003) Fluoroquinolones as antituberculosisagents. In: Rom WN, Garay SM (editors), Tuberculosis, 2ndedition. Philadelphia, PA: Lippincott Williams & Wilkins,pp. 791 807.

3. Rodriguez J, et al. (2001) In vitro activity of fourfluoroquinolones against Mycobacterium tuberculosis. IntJ Antimicrob Agents 17, 229 31.


5. Berning S (2001) The role of fluoroquinolones intuberculosis today. Drugs 61, 9 18.

6. Klemens S, et al. (1994) Activity of levofloxacin in a murinemodel of tuberculosis. Antimicrob Agents Chemother 38,1476 9.

7. Shoen C, et al. (2004) Short-course treatment regimento identify potential antituberculous agents in a murinemodel of tuberculosis. J Antimicrob Chemother 53,641 5].

8. Johnson J, et al. (2006) Early and extended earlybactericidal activity of levofloxacin, gatifloxacin andmoxifloxacin in pulmonary tuberculosis. Int J Tuberc LungDis 10, 605 12.

9. Otani T, et al. (2003) In vitro and in vivo antibacterialactivities of DK-507k, a novel fluoroquinolone. AntimicrobAgents Chemother 47, 3750 9.

10. Kao L, et al. (2006) Pharmacokinetic considerationsand efficacy of levofloxacin in an inhalational anthrax(postexposure) rhesus monkey model. Antimicrob AgentsChemother 50, 3535 42.

11. Product Monograph (2006). Janssen-Ortho Inc., Control #105554.

12. Kang J, et al. (2001) Interactions of a series offluoroquinolone antibacterial drugs with the humancardiac K+ channel HERG. Mol Pharmacol 59, 122 6.

Tuberculosis (2008) 88(2) 122–125

LinezolidGeneric and additional names: LinezolidCAS name: N-[[(5S)-3-[3-fluoro-4-(4-morpholinyl)phenyl]-2-oxo-5-

oxazolidinyl]methyl]acetamideCAS registry #: 165800-03-3Molecular formula: C16H20FN3O4Molecular weight: 337.35Intellectual property rights: Pfizer

ONHN Me

ON

O

F

O

Brand names: Zyvox, Zyvoxid (Pfizer)Derivatives: Dong-A Pharmaceutical has reported several new oxazolidinones (DA-7157, DA-7218 and

DA-7867) having somewhat improved in-vitro potency, compared to linezolid, against Mycobacteriumtuberculosis, M. kansasii and M. marinum1,2

Solubility: In water up to 3 mg/ml [DrugBank]Polarity: Log P 0.232 [DrugBank]Melting point: 181.5 182.5ºC [Merck Index]Formulation and optimal human dosage: Zyvox tablets for oral administration contain 400 mg or 600 mg

linezolid.Zyvox i.v. injection is supplied as a 2 mg/ml isotonic solution for intravenous infusion.Doses: oral or i.v. 600 mg every 12 hours for serious infections and 400 mg every 12 hours for uncomplicatedinfection [FDA label].

Basic biology informationDrug target/mechanism: Linezolid (LIN) is first in anew class of oxazolidinone antibiotics, and inhibitsprotein synthesis by a mechanism not shared byother antibiotics. LIN binds to 23S rRNA inhibitingtranslation in the early phase preventing the properbinding of formyl-methionine tRNA. LIN also inhibitsmammalian mitochondrial protein synthesis, usingisolated mitochondria, with an IC50 of 12.7mg/ml.3

Drug resistance mechanism: No LIN cross-resistancehas been observed with sensitive Mycobacterium tu-berculosis or pan-resistant M. tuberculosis strains.4

Resistance mutations occur in Staphylococcus aureusat the low frequency of 1 in 10 10 to 10 11 andare found in the 23S rRNA [FDA label]. LIN-resistantclinical mutants have been found in S. aureus5 andin the enterococci.6 LIN inhibits bacterial proteinsynthesis through a mechanism of action differentfrom that of other antibacterial agents; therefore,cross-resistance between LIN and other classes ofantibiotics is unlikely. However, a recent publication7

has identified LIN-resistant M. tuberculosis clinicalisolates; specifically, 1.9% of 210 strains had MICsof 4mg/ml (1 strain) and 8mg/ml (3 strains). No

mutations were detected in the following proteinsassociated with the LIN target: 23S rRNA, ribosomalproteins L4 and L22, Erm-37 methyltransferase andWhiB7 putative regulator protein. A mutation in anefflux pump or drug transport is postulated.7

In-vitro potency against MTB: M. tuberculosis H37Rv:MIC 0.25mg/ml.8

Spectrum of activity: LIN is active against a broadrange of Gram-positive organisms and certain Gram-negative species in addition to the mycobacteria.LIN is bacteristatic against enterococci and staphylo-cocci and bactericidal for the majority of strains ofstreptococci.Other in-vitro activity: LIN is active againstM. tuberculosis MDR strains; MIC90s of 1 8mg/mlhave been reported for 39 MDR M. tuberculosisclinical strains, the highest MICs being associatedwith strains resistant to isoniazid (INH), rifampin(RIF), ethambutol (ETH) and streptomycin (STR) orresistant to INH, RIF and ETH.4 The MIC range forLIN against M. bovis including drug-resistant strainsis 0.125 0.5mg/ml.9 The IC50 and IC90 for M. tuber-culosis cultured in macrophages are 32mg/ml and64mg/ml, respectively.10 MPC90 (mutant prevention


LIN

Linezolid 123

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Mouse 0.55*, 0.65** 10.1*, 7.34** 6.5* 0.63 16.3ml/min/kg*

Single dose*10 mg/kg i.v.**10 mg/kg oral15

Rat 1.0±0.1*,1.1±0.3**

15.5±1.6*,42.6±6.6**

15±0.8** 0.72±0.02* 10.5±1.1ml/min/kg*


Rabbit 25.8*, 54.8** Daily dose *50 mg/kg,**75 mg/kg; results at 5 days16

Dog 3.91±0.38*,3.61±0.36**

214±37*,206±51**

67.2±21.2*,28.2±4.1**

0.63±0.05* 1.99±0.33ml/min/kg*


Human 4.26*, 4.4** 91.4*, 80.2** 12.7*, 12.9** 127 ml/min*,138 ml/min**

Single dose*600 mg i.v.**600 mg oral [FDA label]

concentration) for M. tuberculosis is estimated at1.2mg/ml.11

In-vivo efficacy in animal model: In a mouse modelwith drug administered 1 day after infection LIN(100 mg/kg) was less efficacious than INH (25 mg/kg);when drug was given 7 days post infection LIN wasefficacious in a dose-dependent manner but theexperimental oxazolidinone PNU100480 performedbetter.12 LIN reached high concentrations in tissue;PK and susceptibility data indicate that LIN shouldprove useful in TB treatment.11

Efficacy in humansFew clinical studies describing LIN treatment forhuman TB have been published. In two studies, onewith 5 patients (2 patients with M. bovis infectionsand 3 with MDR tuberculosis)13 and another with8 patients,14 individuals infected with MDR-TB whohad been refractory to previous treatment weregiven LIN with other drug combinations. In theFortun study LIN was administered at 600 mg or1200 mg daily; in all cases cultures from respiratorysamples were sterile after 6 weeks of treatment, and3 patients demonstrated clinical and microbiologicalcure after treatment for 5 24 months.13 In theother study 8 HIV-negative patients who had failedat least 3 cycles of TB drugs were treatedwith LIN at 600 mg daily together with otherdrug combinations. The treatments did show someefficacy in terms of culture conversion in all patientsby 82 days; although several individuals died ofrespiratory failure, some completed or were still ontherapy at the time of publication.13 Myelosupressionand peripheral neuropathy were observed in bothstudies, despite an attempt to reduce the dose from1200 mg to 600 mg daily14 to combat these adverseeffects.

LIN is approved for treatment of uncomplicatedand complicated skin and skin-structure infections,pneumonia, nosocomial infections and enterococciincluding sepsis. It is approved for use in children(zyvox FDA label).

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Mouse: Bioavailability 73%.15

• Rat: Bioavailability 100%, widely and evenlydistributed in tissues and plasma.15

• Dog: Bioavailability 97%.15

• Human: Bioavailability ~100%.Plasma protein binding is 31% [FDA label]. Thereis a 1:1 ratio between plasma and inflammatoryfluid.17 Excellent penetration into bronchial mu-cosa and bronchioalveolar fluid was found, withratios of 1:0.79:0.71:8.35 for plasma : bronchialmucosa : macrophages : epithelial lining fluid.18

Animal metabolic pathway: Bioavailability is closeto 100% in rat, dog and human. Protein binding islow, at about 35%, and the drug is well distributedthroughout the body in dog and rat. LIN circulatesin mouse, rat, dog and human mainly as the parentdrug; any circulating metabolites have insignificantantibacterial activity. Between 21% and 34% of thedrug is excreted as the parent compound in mouse,rat and dog; renal excretion is the main eliminationroute in mouse, rat and dog.15

Human metabolic pathway: LIN is metabolized totwo inactive ring-opened forms, aminoethoxyaceticand hydroxyethyl glycine derivatives. 30% of the doseis excreted in urine as LIN and 70% of the dose as thetwo major metabolites, with a small amount presentin faeces (~10% of the dose) also as the metabolites.Little is known about LIN in human milk although the

124 Linezolid

drug is secreted into milk of experimental animals[FDA label].

Safety and TolerabilityAnimal drug drug interactions: LIN does not induce,nor is significantly metabolized by, cytochromeP450 enzymes; neither does it inhibit the clinicallysignificant human CYP isoforms (1A2, 2C9, 2C19, 2D6,2E1, 3A4) [FDA label].Animal toxicity: In adult and juvenile dogs andrats, myelosuppression, reduced extramedullaryhematopoiesis in spleen and liver, and lymphoiddepletion of thymus, lymph nodes, and spleen wereobserved [FDA label].The drug is very evenly distributed throughout thebody in mouse, rat and dog, with tissue and plasmalevels equivalent in many cases.15 Mild reversibleanaemia was caused by treatment of mice with50 mg/kg for 4 days.19

Carcinogenicity: Although lifetime studies in animalshave not been conducted to evaluate the carcino-genic potential of LIN, no mutagenic or clastogenicpotential was found in a battery of tests, includingthe Ames and AS52 assays, an in-vitro unscheduledDNA synthesis (UDS) assay, an in-vitro chromosomeaberration assay in human lymphocytes, and an in-vivo mouse micronucleus assay.Reproductive toxicology: LIN did not affect thefertility or reproductive performance of adult femalerats. It reversibly decreased fertility and reproduc-tive performance in adult male rats when given atdoses 50 mg/kg/day, with exposures approximatelyequal to or greater than the expected humanexposure level (exposure comparisons are based onAUCs). Epithelial cell hypertrophy in the epididymismay have contributed to the decreased fertilityby affecting sperm maturation. Similar epididymalchanges were not seen in dogs. Although theconcentrations of sperm in the testes were in thenormal range, the concentrations in the caudaepididymis were decreased, and sperm from the vasdeferens had decreased motility.Mildly decreased fertility occurred in juvenile malerats treated with LIN through most of their period ofsexual development (50 mg/kg/day from days 7 to36 of age, and 100 mg/kg/day from days 37 to 55of age, with exposures ranging from 0.4-fold to1.2-fold that expected in humans based on AUCs).No histopathological evidence of adverse effects wasobserved in the male reproductive tract [FDA label].Animal safety pharmacology: In rats and dogsthe effect of drug treatment was similar totoxicity observed in humans. Bone-marrow effectswere observed including hypocellularity and de-creased hematopoiesis, decreased extramedullaryhematopoiesis in spleen and liver, and decreased

levels of circulating erythrocytes, leukocytes, andplatelets. Lymphoid depletion occurred in thymus,lymph nodes, and spleen. Generally, the lymphoidfindings were associated with anorexia, weight loss,and suppression of body weight gain [FDA label].Human drug drug interactions: LIN is a reversible,nonselective inhibitor of monoamine oxidase andhas the potential for interaction with adrenergicand serotonergic agents including serotonin re-uptake inhibitors [FDA label], serotonin-boostingantidepressants such as paxil, prozac, and zoloft,as well as other antidepressants such as elavil andtofranil, and decongestants such as sudafed andentex.Over-the-counter cold medicines and cough syrupsthat contain pseudoephedrine can cause druginteractions with LIN.While taking zyvox, it is important to avoideating large amounts of foods that contain thechemical “tyramine”. While taken with a classof antidepressants known as selective serotoninreuptake inhibitors (SSRIs), there is a chance ofdeveloping serotonin syndrome. Symptoms includeeuphoria, drowsiness, rapid muscle contractionand relaxation, restlessness, dizziness, sweating,coordination problems, and fever [FDA label].Human potential toxicity: Myelosuppresion: LINcauses reversible myelosuppression (including an-aemia, leucopenia, pancytopenia, and thrombo-cytopenia) in patients especially when the drug isadministered for prolonged periods of time.Neurotoxicity: Peripheral and optic neuropathy havebeen reported in patients treated with zyvox. Visualblurring has occurred in patients treated with zyvoxfor less than 28 days and visual function tests arerecommended for patients taking this drug for longerthan 3 months [FDA label].Gastrointestinal: acidosis has been reported inpatients treated with zyvox [FDA label].Human adverse reactions: The most commonadverse events in patients treated with zyvox werediarrhoea, headache and nausea [FDA label].

References1. Vera-Cabrera L, et al. (2006) In vitro activities of DA-

7157 and DA-7218 against Mycobacterium tuberculosis andNocardia brasiliensis. Antimicrob Agents Chemother 50,3170 2.

2. Vera-Cabrera L, et al. (2006) In vitro activities of thenovel oxazolidinones DA-7867 and DA-7157 against rapidlyand slowly growing mycobacteria. Antimicrob AgentsChemother 50, 4027 9.

3. McKee E, et al. (2006) Inhibition of mammalianmitochondrial protein synthesis by oxazolidinones.Antimicrob Agents Chemother 50, 2042 9.

4. Erturan Z, Uzun M (2005) In vitro activity of linezolidagainst multidrug-resistant Mycobacterium tuberculosisisolates. Int J Antimicrob Agents 26, 78 80.

LIN

Linezolid 125

5. Tsiodras S, et al. (2001) Linezolid resistance in a clinicalisolate of Staphylococcus aureus. Lancet 358, 207 8.

6. Herrero I, et al. (2002) Nosocomial spread of linezolid-resistant, vancomycin-resistant Enterococcus faecium.N Engl J Med 346, 867 9.

7. Richter E, et al. (2007) First linezolid-resistant clinicalisolates of Mycobacterium tuberculosis. AntimicrobAgents Chemother 51, 1534 6.

8. Acala L, et al. (2003) In vitro activities of linezolid againstclinical isolates of Mycobacterium tuberculosis that aresusceptible or resistant to first-line antituberculous drugs.Antimicrob Agents Chemother 47, 416 7.

9. Tato M, et al. (2006) In vitro activity of linezolidagainst Mycobacterium tuberculosis complex, includingmultidrug-resistant Mycobacterium bovis isolates. Int JAntimicrob Agents 28, 75 8.

10. Sood R, et al. (2005) Activity of RBx 7644 and RBx8700, new investigational oxazolidinones, against My-cobacterium tuberculosis infected murine macrophages.Int J Antimicrob Agents 25, 464 8.

11. Rodriguez J, et al. (2004) Mutant prevention concentra-tion: comparison of fluoroquinolones and linezolid withMycobacterium tuberculosis. J Antimicrob Chemother 53,441 4.

12. Cynamon M, et al. (1999) Activities of several novel

oxazolidinones against Mycobacterium tuberculosis ina murine model. Antimicrob Agents Chemother 43,1189 91.

13. Fortun J, et al. (2005) Linezolid for the treatment ofmultidrug-resistant tuberculosis. J Antimicrob Chemother56, 180 5.

14. Park I, et al. (2006) Efficacy and tolerability of daily-half dose linezolid in patients with intractable multidrug-resistant tuberculosis. J Antimicrob Chemother 58,701 4.

15. Slatter J, et al. (2002) Pharmacokinetics, toxicokinetics,distribution, metabolism and excretion of linezolid inmouse, rat and dog. Xenobiotica 32, 907 24.

16. Dailey C, et al. (2001) Efficacy of linezolid in treatment ofexperimental endocarditis caused by methicillin-resistantStaphylococcus aureus. Antimicrob Agents Chemother 45,2304 8.

17. Gee T, et al. (2001) Pharmacokinetics and tissuepenetration of linezolid following multiple oral doses.Antimicrob Agents Chemother 45, 1843 6.

18. Honeybourne D, et al. (2003) Intrapulmonary penetrationof linezolid. J Antimicrob Chemother 51, 1431 4.

19. Hickey E, et al. (2006) Experimental model ofreversible myelosuppression caused by short-term, high-dose oxazolidinone administration. Therapy 3, 521 6.

Tuberculosis (2008) 88(2) 126

LL-3858Generic and additional names: LL-3858, SudoterbIntellectual property rights: Lupin Ltd

Lupin has identified three compounds that have demonstratedsignificant in vitro and in vivo activity against sensitive andresistant strains of Mycobacterium tuberculosis. Pre-clinicalstudies are in progress [Lupin website, 2006]

N

NH

N N CF3

Me

N

O

Basic biology informationDrug target/mechanism: Not known; LL-3858 is apyrrole derivativeIn-vitro potency against MTB: M. tuberculosis MIC:0.12 0.025mg/ml.1,2

Other in-vitro activity: The compound demonstratesin vitro synergy with rifampin. It is bactericidal in 12days with concentration-dependent killing.1,2 Otherpyrroles have shown activity against TB.3

In-vivo efficacy in animal model: In mouse modelsof 12 weeks duration 12.5 mg/kg LL-3858 showedgood efficacy and complete clearance from lung andspleen not seen with the other compounds tested.No relapse was observed up to 2 months followingthe final dose.1

Efficacy in humansWeb releases (for example Media coverage sum-mary 7 2004) indicate that clinical trials may begin

but the Lupin website does not post any furtherinformation on this compound.

ADME dataPK in mice is better than with INH in terms of half-life, Cmax and AUC.1

References

1. Arora S, et al. (2004) Presented at 44th InterscienceConference on Antimicrobial Agents and Chemotherapy(ICAAC). Presentation F115.

2. Sinha R, et al. (2004) In vivo activity of LL4858 againstMycobacterium tuberculosis. Presented at 44th AnnualInterscience Conference on Antimicrobial Agents andChemotherapy (ICAAC). Abstract F-1116 2004.

3. Deidda D, et al. (1998) Bactericidal activities of thepyrrole derivative BM212 against multidrug-resistant andintramacrophagic Mycobacterium tuberculosis strains.Antimicrob Agents Chemother 42, 3035 7.


MOXI

Tuberculosis (2008) 88(2) 127–131

MoxifloxacinGeneric and additional names: Moxifloxacin HydrochlorideCAS name: 1-Cyclopropyl-6-fluoro-1,4-dihydro-8-methoxy-7-[(4aS,7aS)-

octahydro-6H-pyrrolo[3,4-b]pyridin-6-yl]-4-oxo-3-quinolinecarboxylicacid hydrochloride

CAS registry #: 186826-86-8Molecular formula: C21H24FN3O4·HClMolecular weight: 437.89Intellectual property rights: Bayer

N

CO2H

O

NHN

OMe

F

H

H

Brand names: Actimax (Sankyo); Actira (Bayer); Avelox (Bayer); Octegra (Bayer); Proflox (Esteve); Vigamox(Alcon)

Derivatives: Moxifloxacin is a quinolone/fluoroquinolone antibiotic related to ciprofloxacin, enoxacin,fleroxacin, gatifloxacin, gemifloxacin, grepafloxacin, levofloxacin, lomefloxacin, norfloxacin, ofloxacin,pefloxacin, prulifloxacin, rufloxacin, sparfloxacin, temafloxacin, trovafloxacin, sitafloxacin

Solubility: Soluble in waterPolarity: Log P 2.033 [DrugBank]Melting point: 238 242ºC [DrugBank]Formulation and optimal human dosage: Avelox tablets: containing moxifloxacin hydrochloride (equivalent to

400 mg moxifloxacin).Avelox i.v.: 250 ml latex-free flexibags as a sterile, preservative-free, 0.8% sodium chloride aqueous solutionof moxifloxacin hydrochloride (containing 400 mg moxifloxacin).400 mg daily dose

Basic biology informationDrug target/mechanism: Moxifloxacin (MOXI: 8-meth-oxy-quinolone), and quinolones in general, exerttheir effects by trapping a DNA drug enzymecomplex and specifically inhibiting ATP-dependentenzymes topoisomerase II (DNA gyrase) and topoi-somerase IV. In most bacteria gyrase facilitates DNAunwinding and topoisomerase IV activates decatena-tion. DNA gyrase (reviewed in Champoux 20011), anessential enzyme involved in the replication, tran-scription and repair of bacterial DNA, consists of twocomponents arranged in a GyrA2/GyrB2 complex en-coded by the gyrA and gyrB genes. Topoisomerase IV,encoded by parC and parE, appears to be absentfrom Mycobacterium tuberculosis and from severalother bacteria including Helicobacter pylori andTreponema palladium.2 Recently the single M. tuber-culosis type II topoisomerase has been cloned intoEscherichia coli and exhibits classical supercoilingactivity as well as enhanced decatenation, cleavageand relaxation activities.3 This is presumably thesingle target for MOXI in the mycobacteria.

Drug resistance mechanism: Resistance to MOXIoccurs at a rate of 1.8×10 9 to <1×10 11 in vitrofor Gram-positive bacteria [FDA label]. There isno known cross-resistance between MOXI and otherclasses of antimicrobials, however cross-resistancehas been observed between MOXI and otherfluoroquinolones. Resistance (3 5-fold higher thanwild-type [WT]) can arise in M. tuberculosis fromchanges in either gyrA or gyrB; furthermore specificmutations in gyrA resulted in hypersensitivity toquinolones.4 Most mutations conferring changes indrug sensitivity occur in a quinolone-resistant regionin gyrA and more rarely in gyrB. Both resistanceand hypersensitivity were reflected in the IC50s ofDNA gyrase overexpressed and purified from theconcomitant M. tuberculosis strains.4 Many MDRclinical strains are sensitive to MOXI (resistanceis defined as MIC > 2mg/ml) even where they arealso resistant to ofloxacin (OFL); however severalstrains in the same study were resistant to MOXIand OFL and in these cases the mutation was oftenin gyrA (A94G). The authors conclude that careful


128 Moxifloxacin

monitoring of resistance to MOXI is warranted inclinical settings.5

In-vitro potency against MTB: M. tuberculosis H37Rv:MIC 0.5mg/ml.4

M. tuberculosis H37Rv comparative MICs for quino-lones: ciprofloxacin 0.5mg/ml, OFL 0.71mg/ml,levofloxacin (LEV) 0.35mg/ml, MOXI 0.177mg/ml,gatifloxacin (GATI) 0.125mg/ml.6

Spectrum of activity: MOXI has broad Gram-positive and Gram-negative activity. It shows in-vitro and clinical efficacy against Staphylococcusaureus, Streptococcus pneumoniae, Str. pyogenes,Haemophilus influenzae, H. parainfluenzae, Kleb-siella pneumoniae, Moraxella catarrhalis, Chlamy-dia pneumoniae and Mycoplasma pneumoniae. MOXIhas activity against mycobacteria in addition toM. tuberculosis; MOXI is more active againstM. kansasii than M. avium complex: specifically MIC90for M. avium > M. intracellulare > M. kansasii at 4,2 and 2mg/ml respectively. MIC90 for M. chelonae >M. fortuitum at 16 and 0.5mg/ml, respectively.7

Other in-vitro activity: MPC90 against M. tuberculo-sis strains: MOXI 1mg/ml, LEV 1mg/ml, ciprofloxacin4mg/ml, OFL 2mg/ml.8

MOXI, like other quinolones, is bactericidal. Thebactericidal activity of MOXI against M. tuberculosiswas decreased somewhat when ethambutol (ETH)or high rifampin (RIF) and MOXI were testedtogether, indicating some antagonism between thesedrugs9 although this activity is not necessarilyreflected in vivo;10 antagonism between RIF or chlo-ramphenicol and another quinolone (ciprofloxacin)has been reported previously.11 A comparison ofquinolones, using an in-vitro model designed topredict sterilizing activities, showed MOXI withthe greatest bactericidal effect against slow-growing bacteria, and the best activity againstpersistors.6 MOXI also outperformed other quino-lones when the MPCs and MPC/AUC ratios werecompared.12

In-vivo efficacy in animal model: In a mousemodel designed to mimic human disease, regimenscontaining MOXI/RIF/pyrazinamide (PZA) reducedtreatment time by up to 2 months compared toregimens with isoniazid (INH)/RIF/PZA.13 Similarresults with a stable cure were reached after4 months in mice treated twice weekly withRIF/MOXI/PZA compared to cure in 6 months whendaily treated with RIF/INH/PZA.14 100 mg/kg MOXIin mice gave activity comparable to INH; increaseddose in mice to 400 mg/kg MOXI daily resulted inspleen CFU counts lower than for INH 25 mg/kg(log CFU 1.4 for INH compared with log CFU 0.4for MOXI) although the differences were notstatistically significant.15 AUC/MIC ratio correlatedbest with in-vivo efficacy for the fluoroquinolones

in a mouse model of tuberculosis.16 MOXI in a pro-drug formulation conjugated to danyl-carboxymethylglucan may have advantages in vivo if it can beadministered orally.17

Efficacy in humansHuman trials with MOXI show promise for shorteningtreatment time and reducing toxicity.14 Using earlybactericidal activity (EBA) at 5 days as a com-parator MOXI (400 mg/daily) is as efficacious as INH(300 mg/daily) and better than RIF (600 mg/daily).Using time to reduce viable counts by 50% (vt50) INHoutperformed MOXI and RIF (Rodrıguez et al. 2004,18

see also Lu and Drlica 200319). In a similar study,comparing MOXI or ETH combined with INH/RIF/PZA,patients achieved negative culture status earlierwith the inclusion of MOXI.20

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Human: Bioavailability 90%. Alveolar macrophage/

plasma ratio ~21. MOXI is well absorbed from thegastrointestinal tract. Food has little effect onabsorption. No significant differences in PK dueto gender, race or age are found; no specificstudies in pediatric patients have been reported[FDA label].

Human metabolic pathway: Approximately 52% ofthe oral or intravenous dose is metabolized viaglucuronide and sulphate conjugation. The sulphateconjugate accounts for 38% of the dose, and theglucuronide conjugate accounts for 14% of thedose. Excretion as unchanged drug: 20% in urineand 25% in faeces; 96±4% excretion as knownmetabolites or parent drug. No changes in renalexcretion in patients with decreased renal function[FDA label].

Safety and TolerabilityAnimal drug drug interactions: The cytochromeP450 system is not involved in metabolism ofMOXI. In-vitro studies indicate that MOXI doesnot inhibit CYP3A4, CYP2D6, CYP2C9, CYP2C19 orCYP1A2, indicating that MOXI is unlikely to alterthe pharmacokinetics of drugs metabolized by thesecytochrome P450 isozymes [FDA label].Animal toxicity: The minimal lethal oral dose inmice is 435 758 mg/kg but 1300 mg/kg for rat and1500 mg/kg for cynomolgus monkey. Intravenous LD50is 105 130 mg/kg for mice and 112 146 mg/kg forrat. MOXI is considered moderately toxic after singleoral or i.v. doses.23

Arthropathy: quinolones have been implicated inarthropathy in humans and animals; in juvenile dogsarthropathy was observed at 30 mg/kg for 28 days

MOXI

Moxifloxacin 129

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Mouse 1.3* 184 norm* 137 norm* *9.2 mg/kg oral single dose; Cmaxand AUC normalized to a dose of9.2 mg/kg21,22

Rat 1.3* 310 norm* 312 norm* *9.2 mg/kg oral single dose; Cmaxand AUC normalized to a dose of9.2 mg/kg21,22

Dog 9* 4090 norm* 251 norm* *9.2 mg/kg oral single dose; Cmaxand AUC normalized to a dose of9.2 mg/kg21,22

Monkey 7.2* 760 norm* 86 norm* *9.2 mg/kg oral single dose; Cmaxand AUC normalized to a dose of9.2 mg/kg21,22

Human 12*,11.5 15.6**

618 norm*,36.1±9.1**

430 norm*,3.1±1**

*1.4 mg/kg oral single dose; Cmaxand AUC normalized to a dose of9.2 mg/kg,21,22

**Single 400 mg oral dose in healthyyoung adults [FDA label]

(1.5× normal human dose) but similar symptomswere not seen in adult rats and monkeys at up to500 mg/kg and 135 mg/kg respectively.23

Ocular toxicity: Electroretinographic and histopatho-logic changes were seen at 90 mg/kg/day in anoral 4-week specialized lens study in beagle dogsusing slit lamp and biochemical investigations. Noadverse effects on the lens were observed in 6-monthchronic studies in rats or monkeys at doses as highas 500 mg/kg or 250 mg/kg respectively.23

Generally MOXI shares liabilities with the otherquinolones but without the phototoxicity seen withsparfloxacin.23

Animal safety pharmacology: Cardiovascular: therewere marginal effects on QT interval in dogs duringweek 1 at a dose of 90 mg/kg/day.23

In monkeys using telemeterized evaluation, MOXI hadno significant effect on mean arterial pressure, heartrate, PR or QRS intervals. MOXI produced significantdose-related increases in QTc at doses of 30 mg/kg(Cmax 5.5±0.6mM), 100 mg/kg (Cmax 16.5±1.6mM),and 175 mg/kg (Cmax 17.3±0.7mM) with peak in-creases of 22 (8%), 27 (10%), and 47 (18%) ms,respectively.24

MOXI has an in-vitro human cardiac K channel hERGIC50 of 129mM, which is not as potent an inhibitorof the hERG channel as some other quinolones suchas sparfloxacin (18mM) or grepafloxacin (50mM), butmore potent than the hERG IC50 for LEV (915mM) andOFL (1420mM).25

Human drug drug interactions: The only fluoro-quinolone known to inhibit the P450 system isciprofloxacin inhibiting CYP1A2 (reviewed in Berning200126). Specifically, no changes were observed

in the metabolism of itraconazole, theophylline,warfarin, digoxin, atenolol, oral contraceptives,or glyburide. Itraconazole, theophylline, warfarin,digoxin, probenecid, morphine, ranitidine, andcalcium did not significantly affect the pharmaco-kinetics of MOXI [FDA label]. Antacids and iron-containing products should be avoided 4 hours beforeor after MOXI dosing due to the potential forreduction in the AUC.Human potential toxicity: Cardiovascular events: QTprolongation was observed in 0.1 3% of patients;drugs which exacerbate these symptoms suchas Solatol, a general antiarrhythmic should beavoided [FDA label]. Prolongation of the QT intervalis a general feature of the fluoroquinolones andMOXI does cause QT prolongation which limitsthe maximum dose (reviewed in Falagas et al.200727). Torsades de pointes can be a result ofthe prolongation in QTc (reviewed in Falagas et al.200727). Specifically, MOXI caused a QTc increasewhen given once daily at 400 mg, whereas twicedaily doses of LEV and CIPRO had no effect onthis parameter. However at higher doses all thefluoroquinolones cause an increase in the QTcinterval (reviewed in Falagas et al. 200727). Ina clinical trial of more than 7900 patients nocardiovascular morbidity or mortality attributableto QTc prolongation occurred with MOXI treatment[FDA label].Arthropathy: quinolones are associated with specifictendinitis-type events, and LEV seems to beassociated with the highest rates among these drugs.MOXI is not recommended for treatment of athletesin training. Cessation of treatment usually reverses

130 Moxifloxacin

these effects which may be more serious in theelderly (reviewed in Owens and Ambrose 200528).Hypoglycaemia is mentioned as a possible side effect[FDA label] although few events have been recorded(reviewed in Owens and Ambrose 200528).Phototoxicity is not a clinically relevant event duringMOXI treatment (reviewed in Owens and Ambrose200528).Human adverse reactions: In clinical trials with6700 patients receiving the 400 mg dose, adverseevents reported in MOXI trials were described asmild to moderate in severity. MOXI was discontinueddue to adverse reactions thought to be drug-related in 3.6% of orally treated patients. Adversereactions, judged by investigators to be at leastpossibly drug-related, occurring in greater thanor equal to 3% of MOXI-treated patients werenausea (7%), diarrhoea (6%) and dizziness (3%).Additional clinically relevant events that occurred in0.1% to <3% of patients were:

body as a whole: abdominal pain, headache, as-thenia, injection site reaction (including phlebitis),malaise, moniliasis, pain, allergic reaction;cardiovascular: tachycardia, palpitation, vasodila-tion, QT interval prolonged;digestive: vomiting, abnormal liver function test,dyspepsia, dry mouth, flatulence, oral moniliasis,constipation, GGTP increased, anorexia, stomati-tis, glossitis;haemic/lymphatic: leukopenia, eosinophilia, pro-thrombin decrease (prothrombin time prolonged/International Normalized Ratio (INR) increased),thrombocythemia;metabolic/nutritional: lactic dehydrogenase in-creased, amylase increased;muscular: arthralgia, myalgia;CNS: insomnia, nervousness, vertigo, somnolence,anxiety, tremor;skin: rash (maculopapular, purpuric, pustular),pruritus, sweating, urticaria;special senses: taste perversion;urogenital: vaginal moniliasis, vaginitis [FDA la-bel].

References

1. Champoux J (2001) DNA topoisomerases: structure,function, and mechanism. Annu Rev Biochem 70, 369413.

2. Gordon S, et al. (2001) Genomics of Mycobacterium bovis.Tuberculosis 81(1 2), 157 63.

3. Aubry A, et al. (2006) First functional characterizationof a singly expressed bacterial type II topoisomerase:the enzyme from Mycobacterium tuberculosis. BiochemBiophys Res Commun 348, 158 65.

4. Aubry A, et al. (2006) Novel gyrase mutations inquinolone-resistant and -hypersusceptible clinical isolates

of Mycobacterium tuberculosis: functional analysis ofmutant enzymes. Antimicrob Agents Chemother 50,104 12.

5. Kam K, et al. (2006) Stepwise decrease in moxifloxacinsusceptibility amongst clinical isolates of multidrug-resistant Mycobacterium tuberculosis: correlation withofloxacin susceptibility. Microb Drug Res 12, 7 11.


7. Rodriguez Diaz J, et al. (2003) In vitro activity ofnew fluoroquinolones and linezolid against nontuberculousmycobacteria. Int J Antimicrob Agents 21, 585 8.

8. Rodrıguez J, et al. (2001) In vitro activity of fourfluoroquinolones against Mycobacterium tuberculosis. IntJ Antimicrob Agents 17, 229 31.

9. Lu T, Drlica K (2003) In vitro activity of C-8-methoxyfluoroquinolones against mycobacteria when combinedwith anti-tuberculosis agents. J Antimicrob Chemother 52,1025 8.

10. Alvirez-Freites E, et al. (2002) In vitro and in vivo activitiesof gatifloxacin against Mycobacterium tuberculosis.Antimicrob Agents Chemother 46, 1022 5.

11. Gradelski E, et al. (2001) Activity of gatifloxacin andciprofloxacin in combination with other antimicrobialagents. Int J Antimicrob Agents 17, 103 7.

12. Rodrıguez J, et al. (2004) Mutant prevention concentra-tion: comparison of fluoroquinolones and linezolid withMycobacterium tuberculosis. J Antimicrob Chemother 53,441 4.

13. Nuermberger E, et al. (2004) Moxifloxacin-containingregimen greatly reduces time to culture conversion inmurine tuberculosis. Am J Respir Crit Care Med 169,421 6.

14. Rosenthal I, et al. (2006) Potent twice-weekly rifapentine-containing regimens in murine tuberculosis. Am J RespirCrit Care Med 174, 94 101.

15. Yoshimatsu T, et al. (2002) Bactericidal activity ofincreasing daily and weekly doses of moxifloxacin inmurine tuberculosis. Antimicrob Agents Chemother 46,1875 9.

16. Shandil R, et al. (2007) Moxifloxacin, ofloxacin,sparfloxacin, and ciprofloxacin against Mycobacteriumtuberculosis: evaluation of in vitro and pharmacodynamicindices that best predict in vivo efficacy. AntimicrobAgents Chemother 51, 576 82.

17. Schwartz Y, et al. (2006) Novel conjugate of moxifloxacinand carboxymethylated glucan with enhanced activityagainst Mycobacterium tuberculosis. Antimicrob AgentsChemother 50, 1982 8.

18. Gosling R, et al. (2003) The bactericidal activity ofmoxifloxacin in patients with pulmonary tuberculosis. AmJ Respir Crit Care Med 168, 1342 5.

19. Pletz M, et al. (2004) Early bactericidal activity ofmoxifloxacin in treatment of pulmonary tuberculosis:a prospective, randomized study. Antimicrob AgentsChemother 48, 780 2.

20. Burman W, et al. (2006) Moxifloxacin versus ethambutol inthe first 2 months of treatment for pulmonary tuberculosis.Am J Respir Crit Care Med 174, 331 8.

21. Siefert H, et al. (1999) Pharmacokinetics of the 8-methoxyquinolone, moxifloxacin: tissue distribution inmale rats. J Antimicrob Chemother 43(Suppl B), 61 7.

22. Siefert H, et al. (1999) Pharmacokinetics of the 8-methoxyquinolone, moxifloxacin: a comparison in humanand other mammalian species. J Antimicrob Chemother43(Suppl B), 69 76.

MOXI

Moxifloxacin 131

23. von Keutz E, Schluter G (1999) Preclinical safetyevaluation of moxifloxacin, a novel fluoroquinolone.J Antimicrob Chemother 43, 91 100.

24. Chaves A, et al. (2006) Cardiovascular monkey telemetry:Sensitivity to detect QT interval prolongation J PharmacolToxicol Methods 54, 150 8.

25. Kang J, et al. (2001) Interactions of a series offluoroquinolone antibacterial drugs with the humancardiac K+ channel HERG. Mol Pharmacol 59, 122 6.

26. Berning S (2001) The role of fluoroquinolones intuberculosis today. Drugs 61, 9 18.

27. Falagas M, et al. (2007) Arrhythmias associated withfluoroquinolone therapy. Int J Antimicrob Agents 29,374 9.

28. Owens R, Ambrose P (2005) Antimicrobial safety: focus onfluoroquinolones. Clin Infect Dis 41(Suppl 2), S144 57.

Tuberculosis (2008) 88(2) 132–133

OPC-67683Generic and additional names: OPC-67683CAS name: (R)-2-Methyl-6-nitro-2-{4-

[4-(4-trifluoromethoxyphenoxy)piperidin-1-yl]-phenoxymethyl}-2,3-dihydroimidazo[2,1-b]-oxazole

CAS registry #: 681492-22-8Molecular formula: C25H25N4F3O6Molecular weight: 534.48Intellectual property rights: Otsuka Pharmaceuti-

cal Co., Ltd.

N

N

O2N

O Me

O

N

O

OCF3

Brand names: N/ADerivatives: See structurally similar compound PA-824Solubility: WaterFormulation and optimal human dosage: A patent for OPC-67683 was filed by Otsuka in 2003. A phase I OPC-

67683 clinical trial was performed in Japan in early 2006, but results are currently unavailable. Otsukafiled a patent through the Patent Cooperative Treaty (PCT) process to cover 2,3-dihydro-6-nitroimidazo-(2,1-b)oxazole compounds for TB treatment.

Basic biology informationDrug target/mechanism: OPC-67683 is closely re-lated to PA-824 and may share a similar mode ofaction. The compound has been shown to inhibitmycolic acid biosynthesis and kill Mycobacteriumtuberculosis in vitro. Similar to PA-824, OPC-67683 isa prodrug and requires activation by M. tuberculosisfor activity; experimentally isolated OPC-67683-resistant mycobacteria did not metabolize the com-pound and a mutation in the M. tuberculosis Rv3547gene (responsible for activating PA-824) amongthe resistant organisms suggests that this enzymeis involved in activating OPC-67683.1 Matsumotoet al.1 suggest the possibility that generation of aradical intermediate during drug activation could beresponsible for the killing activity of OPC-67683.1

OPC-67683 inhibits mycolic acid synthesis, specif-ically inhibiting incorporation of 14C-acetate andfatty acid. IC50 of 21 and 36 ng/ml for incorporationinto methoxy- and ketomycolate respectively werereported. Changes in the morphology of the cell wallwere observed.2

Drug resistance mechanism: OPC-67683 is activeagainst strains resistant to rifampin (RIF), etham-butol (ETH), pyrazinamide (PZA), isoniazid (INH)and streptomycin (STR).1 A spontaneous mutation

rate is not available. Mutations in M. tubercu-losis Rv3547, the gene responsible for activatingPA-824, have been found among experimentallygenerated resistant organisms.1 See also the Drugtarget/mechanism section.In-vitro potency against MTB: M. tuberculosis H37Rv:MIC 0.012mg/ml.1

Spectrum of activity: OPC-67683 is describedas mycobacteria specific.1 It is active againstM. kansasii and M. tuberculosis while PA-824 showedactivity only against M. tuberculosis.3

Other in-vitro activity: Activity (MIC) of OPC-67683against INH-, RIF-, ETH- and STR-resistant strainsof M. tuberculosis was unchanged from the activityof OPC-67683 against the wild-type control. Noevidence of antagonism was observed when OPC-67683 was examined in vitro in combination withother known TB drugs (RIF, INH, ETH, STR). Intra-cellular post-antibiotic activity was estimated usingthe H37Rv strain in THP1 cells; OPC-67683 activity at0.1mg/ml was equal to RIF at 3mg/ml and superior toINH and PA-824. Results suggest that even brief expo-sure to the drug may kill M. tuberculosis in cells.1

In-vivo efficacy in animal model: OPC-67683 is orallyactive in a mouse lung model. Daily dosing regimen(beginning 28 days post i.v. infection) for 28 days:


OPC

OPC-67683 133

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Mouse 5.9 5.7 0.43 Data for mouse PK given at 3 mg/kgsingle dose oral.4

Rat 6.4 7.5 0.50 Data for rat PK given at 3 mg/kgsingle dose oral.4

Dog 17 8.3 0.33 Data for dog PK given at 3 mg/kgsingle dose oral.4

CFU reduction of >95% was achieved using OPC-67683, RIF, INH, ETH, STR and PZA at 0.625, 3.5,5, >160, 40 and 160 mg/kg, respectively;1 similarresults were seen in BALB/c nude or immuno-competent mice.1 In long-term treatments over 6months, regimens including OPC-67683 were superiorto regimens without OPC-67683, and indicated thatthis drug could reduce the length of treatment byup to 2 months. Specifically, mice were treatedwith OPC-67683, RIF and PZA for 2 months followedby OPC-67683 for another 2 months; alternatelymice were treated with RIF, INH, ETH and PZA for2 months followed by RIF and INH for 4 months.Drugs were used at: OPC 2.5 mg/kg, RIF 5 mg/kg,PZA 100 mg/kg, ETH 100 mg/kg, and INH 10 mg/kg.At 3 months after start of therapy colonies wereseen in 1/6 of the OPC-treated mice and in 0/6at 4 months, whereas all the animals using thealternate regime were still showing signs of infectionat 4 months.1

Efficacy in humansPhase I and Phase II studies have been conducted butresults are not available.

ADME dataSee table 1 for main PK characteristics. AdditionalADME data are also provided by Matsumoto et al.1

Other ADME data:• Mouse: 42% orally bioavailable. Following 3 mg/kg

single oral dose in mice: Cmax plasma 0.4mg/ml <lung 1.3mg/ml (Miyamoto et al. 2005,4 also seeMatsumoto et al. 20061).

• Rat: 35% orally bioavailable. Drug concentrationsfollowing 3 mg/kg single oral dose in rat: Liver >kidney > heart, lung > plasma, spleen (Miyamotoet al. 2005,4 also see Matsumoto et al. 20061).

• Dog: 60% orally bioavailable (Miyamoto et al.2005,4 also see Matsumoto et al. 20061).

• Human: In vitro OPC-67683 was not metabolized toany significant extent by human liver microsomes,

and there was no effect on CYP enzyme activitiesat levels up to 100mM.1

Animal metabolic pathway: OPC-67683 was notsignificantly metabolized by liver microsomes andno major metabolites were identified in any of thespecies tested using labeled or unlabeled drug.4

OPC-67683 was significantly metabolized after ex-posure to M. bovis BCG strain, giving one majormetabolite, the desnitro-imidazooxazole.1

Safety and TolerabilityAnimal drug drug interactions: OPC-67683 was notan inhibitor of CYP enzymes using liver microsomalpreparations.1

Animal toxicity: Other similar compounds such asmetronidazole are mutagenic, but OPC-67683 wasfound not to be genotoxic; there was no correlationbetween mutagenicity and the antibacterial proper-ties.1,5

References

1. Matsumoto M, et al. (2006) OPC-67683, a nitro-dihydro-imidazooxazole derivative with promising action againsttuberculosis in vitro and in mice. PLoS Med 3(11): e466.doi:10.1371/journal.pmed.0030466.

2. Kawasaki M, et al. (2005) Mechanism of action of OPC-67683 against M. tuberculosis. Presented at InterscienceConference on Antimicrobial Agents and Chemotherapy(ICAAC), Washington, DC. Poster F-1463.

3. Doi N, Disratthakit A (2006) Characteristic anti-mycobacterial spectra of the novel anti-TB drug candi-dates OPC-67683 and PA-824. Presented at InterscienceConference on Antimicrobial Agents and Chemotherapy(ICAAC), San Francisco, CA. Poster F1-1377a.

4. Miyamoto G, et al. (2005) Unique PK profile of OPC-67683, a new potent anti-tuberculous drug. Presentedat Interscience Conference on Antimicrobial Agents andChemotherapy (ICAAC), Washington, DC. Poster F-1466.

5. Hashizume H, et al. (2005) 67683, a novel imidazo-oxazole derivative, free from mutagenicity. Presentedat Interscience Conference on Antimicrobial Agents andChemotherapy (ICAAC), Washington, DC. Poster F-1464.

Tuberculosis (2008) 88(2) 134–136

PA-824Generic and additional names: PA-824CAS name: (3S)-8-nitro-3-[[4-(trifluoromethoxy)phenyl]methoxy]-

5-oxa-1,7-diazabicyclo[4.3.0]nona-6,8-dieneMolecular formula: C14H12F3N3O5Molecular weight: 359Intellectual property rights: TB Alliance and Novartis

N

N O

O

OCF3

O2N

Derivatives: See structurally similar compound OPC-67683. The TB Alliance has also initiated an investigationof PA-824 nitroimidazole analogs, currently in the discovery phase of development [TB Alliance]

Polarity: Log P 3.393Formulation and optimal human dosage: Not approved for use in humans.

Basic biology informationDrug target/mechanism: PA-824 possibly acts viageneration of radicals having non-specific toxiceffects; however the drug has been shown to inhibitmycolic acid and protein biosynthesis.1

Specific inhibition of mycolic acid and protein syn-thesis: using Mycobacterium bovis BCG strain, in thepresence of PA-824, protein synthesis (incorporationof 35S) and lipid synthesis (uptake of 14C-acetateinto mycolic acid precursors) were both inhibitedin a drug-dependent manner.1 Concentrations ofhydroxymycolate, a precursor for ketomycolate,rose significantly under low drug (<1mg/ml) butfell as drug concentrations increased; ketomycolateconcentrations decreased with increasing drug,suggesting that PA-824 might act at or around thismetabolic step. Protein synthesis was also inhibitedin a drug-dependent manner but an intriguingaccumulation in labeled proteins at <1mg/ml drugremains to be explained.1

Non-specific effects: the related compound metro-nidazole, an antibacterial and antiprotozoal drug,is thought to act by damaging DNA; a RecR mutantin M. bovis BCG strain was more sensitive tometronidazole compared to WT (Sander et al. 2001,2

reviewed in Samuelson 19993). PA-824 may alsoexhibit some of its effects through the generationof radicals.4,5

PA-824 activation: PA-824 is active as the reducedform of the parent drug, requiring cofactor-420-dependent glucose-6-phosphate dehydrogenase(FGD1) reduction of an aromatic nitro group. Cofac-tor 420 (F420) is a flavin-containing molecule with

limited distribution in the archaea and Gram-positivebacteria.1 In vitro oxidized F420 was reduced bypartially purified FDG1 in the presence of glucose-6-phosphate; addition of PA-824 neither inhibitedthe reaction nor was PA-824 itself metabolized,indicating that another as yet unknown factor isrequired for activation.6

Drug resistance mechanism: In vitro resistance fre-quency with PA-824 in M. tuberculosis is ~6.5×10 7,equivalent to isoniazid (INH);6 no cross-resistancewith other known mechanisms has been identified.Target directed mutants: no mutants outside thedrug activating pathway have been reported todate.Drug activating pathway: Mutations in some ofthe genes encoding the PA-824 activating ma-chinery, F420-dependent glucose-6-phosphate de-hydrogenase and F420 biosynthesis pathway geneRv1173, have been shown to be resistant to PA-824.Intriguingly mutants in another gene of unknownfunction, Rv3547, were resistant to PA-824 butsensitive to a closely related analog CGI-17341; thissuggests that Rv3547 may be able to bind drug anddistinguish between the related analogs based ondifferential affinity.6

In-vitro potency against MTB: M. tuberculosis H37RvMICs: 0.15 0.3mg/ml6 and 0.13mg/ml1 compared toINH 0.03mg/ml.Spectrum of activity: PA-824 has very specificactivity, possibly due to its unique reducing activity;it appears to be limited to the MTB complex as thereis very limited efficacy against M. smegmatis andM. avium.7 Weak activity against M. ulcerans has


PA-824

PA-824 135

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Mouse 12.8±1 (S);18.3±1 (M)

327.6±77.1 (S);396.8±97.9 (M)

21.4±5.7 (S);25±3.6 (M)

Single (S) or 5 oral doses/week for 2months (M) in mice using100 mg/kg.13

been reported,8 and M. leprae is resistant to PA-824presumably because it lacks the gene encodingRv3547.9 OPC-67683 is active against M. kansasii andM. tuberculosis while PA-824 showed activity onlyagainst M. tuberculosis.10

Other in-vitro activity: PA-824 is bactericidal againstreplicating and non-growing M. tuberculosis.1 MICsfor PA-824 were superior to INH when testedagainst a panel of drug-resistant clinical isolates.11

Bactericidal activity at 4-fold MIC was evidentfollowing post-treatment drug dilution.1 Activity ofPA-824 against M. tuberculosis under reduced oxygentension was equivalent to that of metronidazole;the latter is a related compound known to inhibitgrowth of non-replicating M. tuberculosis underanaerobic conditions. CGI-17341, a mutagenic com-pound related to PA-824, was much less efficacious,having even less activity than INH, which is knownto be relatively inactive under these anaerobicconditions.1

PA-824 MIC90 against 29 M. ulcerans isolates was>16mg/ml.8

In-vivo efficacy in animal model: PA-824 has potentactivity during the continuation treatment phase,indicating that it is active against persistent bacilliand has the potential to shorten therapy.12

PA-824 has oral activity against both replicating andnon-replicating forms of M. tuberculosis.12 Com-pared with 328 related nitroimidazopyrans PA-824demonstrated the best in vivo activity at 25 mg/kg inmice, suggesting superior PK.1 At 10 days treatmentin a mouse model (both lung and spleen burdensmonitored) using 25 mg/kg, PA-824 was equivalent toINH (25 mg/kg); it also equaled INH over a 28-daydosing period in a guinea pig model where drugdosing was delayed for 30 days post infection. Ineach case the window between toxicity and efficacywas significant.1 PA-824 demonstrated activity in thecontinuation phase equivalent to rifampin (RIF)/INH:both treatments showed sterilizing activity in anin vivo model with 2 months dosing RIF/INH/pyrazinamide (PZA) followed by 4 months dosingwith RIF/INH or PA-824.12 Selection of resistantmutants was reduced when PA-824 and INH werecoadministered.12

PA-824 failed to protect against M. ulcerans in afootpad model.8

Efficacy in humansStudies are ongoing.

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Mouse: Concomitant dosing of RIF/PZA/INH with

PA-824 did not significantly affect the PK for thelatter and had minimal effects on RIF/INH PK.

• Monkey: 40% bioavailability [TB Alliance].

Safety and TolerabilityAnimal toxicity: Toxic thresholds in mice: 1000 mg/kgsingle dose and 500 mg/kg daily dose for 28 days.1

Compounds in the nitroimidazole series have beendescribed as radiosensitizers which selectivelysensitize hypoxic cells to the lethal effect ofradiation. The analog CGI-17341 has been shownto be mutagenic,1,7 however PA-824 lacks themutagenic properties previously associated withbicyclic nitroimidazoles. Using 100 mg/kg, 5 oraldoses/week for 2 months in mice no change inorgan weight was found compared to untreatedcontrols.11 14-days repeat dose studies in monkeyand rat have been completed but data not released[TB Alliance].Human drug drug interactions: Minimal potential toinduce P450 enzymes [TB Alliance].Human adverse reactions: PA-824 is not yet approvedfor human use but is in clinical trials.

References1. Stover K, et al. (2000) A small-molecule nitroimidazopyran

drug candidate for the treatment of tuberculosis. Nature405, 962 6.

2. Sander P, et al. (2001) Mycobacterium bovis BCG recAdeletion mutant shows increased susceptibility to DNA-damaging agents but wild-type survival in a mouseinfection model. Infect Immun 69, 3562 8.

3. Samuelson J (1999) Why metronidazole is active againstboth bacteria and parasites. Antimicrob Agents Chemother43, 1533 41.

4. Bollo S, et al. (2004) Electrogenerated nitro radicalanions: A comparative kinetic study using scanningelectrochemical microscopy. J Electrochem Soc 151,E322 5.

5. Edwards D (1993) Nitroimidazole drugs Actionand resistance mechanisms. I. Mechanisms of action.J Antimicrob Chemother 31, 9 20.

136 PA-824

6. Manjunatha U, et al. (2006) Identification of anitroimidazo-oxazine-specific protein involved in PA-824resistance in Mycobacterium tuberculosis. Proc Natl AcadSci USA 103, 431 6.

7. Ashtekar D, et al. (1993) In vitro and in vivo activitiesof the nitroimidazole CGI 17341 against Mycobacteriumtuberculosis. Antimicrob Agents Chemother 37, 183 6.

8. Ji B, et al. (2006) In vitro and in vivo activities of rifampin,streptomycin, amikacin, moxifloxacin, R207910, linezolid,and PA-824 against Mycobacterium ulcerans. AntimicrobAgents Chemother 50, 1921 6.

9. Manjunatha U, et al. (2006) Mycobacterium lepraeis naturally resistant to PA-824. Antimicrob AgentsChemother 50, 3350 4.

10. Doi N, Disratthakit A (2006) Presented at Interscience

Conference on Antimicrobial Agents and Chemotherapy(ICAAC), San Francisco, CA. Poster F1-1377a.

11. Lenaerts A, et al. (2005) Preclinical testing ofthe nitroimidazopyran PA-824 for activity againstMycobacterium tuberculosis in a series of in vitro andin vivo models. Antimicrob Agents Chemother 49, 2294301.

12. Tyagi S, et al. (2005) Bactericidal activity of the nitro-imidazopyran PA-824 in a murine model of tuberculosis.Antimicrob Agents Chemother 49, 2289 93.

13. Nuermberger E, et al. (2006) Combination chemotherapywith the nitroimidazopyran PA-824 and first-line drugsin a murine model of tuberculosis. Antimicrob AgentsChemother 50, 2621 5.

PAS

Tuberculosis (2008) 88(2) 137–138

Para-aminosalicylic acidGeneric and additional names: para-aminosalicylic acid; PASCAS name: 4-Amino-2-hydroxybenzoic acidCAS registry #: 65-49-6Molecular formula: C7H7NO3Molecular weight: 153.14Intellectual property rights: Generic, marketed 1946

CO2H

OH

NH2

Brand names: PASER (Jacobus); Rezipas (Bristol-Myers Squibb)Derivatives: Schiff-base analogs of PAS with improved activity have been reported1

Solubility: One gram dissolves in about 500 ml water, in 21 ml alcohol. Slightly soluble in ether. Practicallyinsoluble in benzene. Soluble in dilute nitric acid or dilute sodium hydroxide [Merck Index].

Polarity: Log P 1.012 [DrugBank]Acidity/basicity: pKa 3.25; pH of 0.1% aq solution: 3.5 [Merck Index].Melting point: 150.5ºC [DrugBank]Formulation and optimal human dosage: Tablet 500 mg, dose is 8 12 g daily in 2 3 doses. Peloquin et al.2

describe the advantages of twice daily dosing with granules as opposed to once daily dosing.

Basic biology informationDrug target/mechanism: Para-aminosalicylic acid(PAS) was previously thought to target dihydro-pteroate synthase (DHPS), the target of sulfonamidedrugs, but Nopponpunth et al.3 demonstrated thatPAS was a poor in vitro inhibitor of the enzyme.Rengarajan et al.4 demonstrated that transposon-directed disruption of the Mycobacterium bovisthymidylate synthase gene, thyA, results in resis-tance to PAS and an MIC of >27mg/ml; enzymeactivity of thymidylate synthase in the PAS-resistanttransposon mutants was reduced. Evidence from a1975 paper indicates that PAS could interfere withiron acquisition by the bacteria. Recent data5 on ABCtransporters and virulence in M. tuberculosis andcarboxymycobactin inhibitors could renew interestin the area of iron uptake in mycobacteria as a drugtarget.Drug resistance mechanism: Mutations in thyA havebeen found in M. tuberculosis PAS-resistant clinicalisolates.4

In-vitro potency against MTB: M. tuberculosis H37Rv:MIC90 0.3 1mg/ml.3

Spectrum of activity: PAS is used with other anti-tuberculosis drugs (most often isoniazid [INH]) forthe treatment of all forms of active tuberculosis[DrugBank]. Some renewed interest in PAS as asecond-line TB treatment results from relatively

infrequent use of this drug in the clinic andconcomitant lack of resistance.4

Other in-vitro activity: PAS is bacteristatic. Theaminosalicylic acid MIC for M. tuberculosis in 7H11agar was <1.0mg/ml for nine strains including threemultidrug-resistant (MDR) strains, but 4 and 8mg/mlfor two other MDR strains. PAS is inactive in vitroagainst M. avium [DrugBank].In-vivo efficacy in animal model: The free drug hasa short serum half-life of one hour. It is desirable tokeep drug serum concentrations above 1mg/ml dueto lack of post-antibacterial effect and bacteristaticnature. The drug may require a twice-daily dosingregimen.

Efficacy in humansPAS is now mostly used as a second-line drug for thetreatment of MDR M. tuberculosis; it was consideredfirst line but was replaced by ethambutol (ETH) in theearly 1960s.6 It is bacteristatic but may help to slowdevelopment of resistance to other drugs, especiallyINH and streptomycin (STR) [DrugBank].

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Rat: Rats given 5 mg PAS by inhalation had a peak

lung concentration of 10× MIC. Normalizing this


138 Para-aminosalicylic acid

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Human 0.75 1 9 35(median 20)

Single 4 g dose in healthy adults.A level above 1mg/ml wasmaintained for 8 hours [DrugBank].

and comparing to human dose gives efficacy at11 mg/kg compared to 57 mg/kg needed for oraldosing.7

• Human: Following a comparison of once- ortwice-daily (4 g) dosing Peloquin et al.2 recom-mend a twice-daily dose to maintain drug about1mg/ml for the treatment of MDR-TB.50 60% is protein bound [DrugBank]. AdministeringPAS with food increases the Cmax by 50% and theAUC by 70%; divalent cations reduced Cmax andAUC.8

Human metabolic pathway: Within 2 hours of dosingup to 10% of the drug is acetylated in the stomachto N-acetylated PAS, a known hepatotoxin. 80% ofdrug is excreted in the urine with half of this as theacetylated form [DrugBank].

Safety and TolerabilityAnimal toxicity: LD50 orally in mice: 4 g/kg. LD50orally in rabbits: 3.650 g/kg [DrugBank].Human drug drug interactions: PAS may decreasethe amount of digoxin and vitamin B12; vitamin B12supplement may be required [DrugBank].Human potential toxicity: Metabolism of PASproduces a toxic inactive metabolite under acidconditions [DrugBank].Gastrointestrinal: toxicity included gastrointestinalevents leading to poor compliance (described in Ren-garajan et al. 20044). The currently available granuleformulation reduces nausea; it is recommended totake the granules with acid beverage.2

Human adverse reactions: PAS is contraindicated forpatients with serious renal disease due to build up oftoxic metabolites, especially the acetylated forms.PAS interferes with uptake of vitamin B12 andwith thyroid metabolism. Vitamin supplements can

reverse the former issue and thyroxine reverses thelatter [DrugBank].Dermatological side effects: skin rash, erythema-tous, maculopapular and pruritic lesions oftenstarting on face and neck (reviewed in Wilson et al.20039).Other toxicities: lymphadenopathy, jaundice, leuko-cytosis, conjunctivitis, headaches and joint pains(reviewed in Wilson et al. 20039).

References1. Patole J, et al. (2006) Schiff base conjugates of

p-aminosalicylic acid as antimycobacterial agents. BioorgMed Chem Lett 16, 1514 7.

2. Peloquin C, et al. (1998) Once-daily and twice-daily dosingof p-aminosalicylic acid granules. Am J Respir Crit CareMed 159, 932 4.

3. Nopponpunth V, et al. (1999) Cloning and expression ofMycobacterium tuberculosis and Mycobacterium lepraedihydropteroate synthase in Escherichia coli. J Bacteriol181, 6814 21.

4. Rengarajan J, et al. (2004) The folate pathway is a targetfor resistance to the drug para-aminosalicylic acid (PAS)in mycobacteria. Mol Microbiol 53, 275 82.

5. Rodriguez G, Smith I (2006) Identification of an ABCtransporter required for iron acquisition and virulence inMycobacterium tuberculosis. J Bacteriol 188, 424 30.


7. Tsapis N, et al. (2003) Direct lung delivery of para-aminosalicylic acid by aerosol particles. Tuberculosis 83,379 85.

8. Burman W (2003) PK considerations and drug drug inter-actions in tuberculosis treatment. In: Rom WN, Garay SM(editors), Tuberculosis, 2nd edition. Philadelphia, PA:Lippincott Williams & Wilkins, pp. 809 822.

9. Wilson J, et al. (2003) Para-aminosalicylic acid (PAS)desensitization review in a case of multidrug-resistantpulmonary tuberculosis. Int J Tuberc Lung Dis 7, 493 7.

PRO

Tuberculosis (2008) 88(2) 139–140

ProthionamideGeneric and additional names: Prothionamide; 2-propylthioisonicotinamide;

prothionamide; 2-propyl-4-thiocarbamoylpyridineCAS name: 2-Propyl-4-pyridinecarbothioamideCAS registry #: 14222-60-7Molecular formula: C9H12N2SMolecular weight: 180.27Intellectual property rights: Generic

N

NH2S

Me

Derivatives: Prothionamide is the propyl analog of ethionamideSolubility: Soluble in ethanol, methanol; slightly soluble in ether, chloroform; practically insoluble in water

[Merck Index].Formulation and optimal human dosage: 250 g tablet, 500 750 mg daily

Basic biology informationDrug target/mechanism: Prothionamide (PRO), seeethionamide (ETA).Drug resistance mechanism: There is complete cross-resistance between PRO and ETA, and resistanceemerges rapidly.1

In-vitro potency against MTB: MIC Mycobacteriumtuberculosis H37Rv: ~0.5mg/ml.2

Spectrum of activity: PRO has activity againstmycobacterial species including M. leprae andM. avium.2 PRO killed M. leprae more quickly thandid ETA.3

Other in-vitro activity: See ETA. ETA and PRO arebactericidal.2

In-vivo efficacy in animal model: PRO is as active asETA against M. tuberculosis in mice.4 See also ETA.

Efficacy in humansPRO is used interchangeably with ETA accordingto Wang et al.2 In a clinical trial with leprosypatients PRO (250 or 500 mg/day) outperformed ETAat the same dose.3 PRO has been reported as bettertolerated than ETA in humans.4

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Human: PRO, like ETA, is rapidly eliminated, with

the half-life for PRO being slightly less than forETA. Plasma concentrations for PRO are less thanfor ETA.4

Human metabolic pathway: Conversion to the activesulfoxide metabolite takes place with PRO andETA; the sulfoxides are then metabolized to thenicotinamide and nicotinic acid forms, both of whichhave no anti-bacterial activity. Other metabolitessuch as N-methylation and oxidation of the pyridinering are also formed. Of the total dose given, 0.16% isexcreted as PRO and 1.2% excreted as PRO sulfoxide;less than 0.1% is excreted unchanged in the faeces.4

Safety and TolerabilityAnimal toxicity: LD50 in mice, rats (g/kg): 1.0, 1.32orally [Merck Index].Human drug drug interactions: Hepatotoxicity isconsiderably increased when PRO is used in combi-nation therapy with rifampicin and thiacetazone.5

Human potential toxicity: PRO has been describedas more toxic1 or less toxic4 than ETA. PRO shouldbe avoided during pregnancy or in women of child-bearing potential unless the benefits outweigh itspossible hazards.5

Human adverse reactions: Most common adversereactions are dose-related gastrointestinal distur-bances, anorexia, excessive salivation, a metallictaste, nausea, vomiting, abdominal pain and diar-rhoea.CNS disturbances include depression, anxiety, psycho-sis, headache, postural hypotension and asthenia.Peripheral and optic neuropathy and pellagra-likesyndrome have occurred.Hepatitis may occur especially when given inassociation with rifampicin.


140 Prothionamide

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Human 1.38 250 mg dose in humans. Cmax forETA is about 1.8 times higher thanfor PRO, with the same ratios beingobserved for the sulfoxidemetabolites.4

Other side effects include hypersensitivity reac-tions, alopecia, dermatitis, endocrine disturbances,hypoglycaemia, and hypothyroidism with or withoutgoiter.5

References1. Di Perri G, Bonora S (2004) Which agents should we use

for the treatment of multidrug-resistant Mycobacteriumtuberculosis?J Antimicrob Chemother 54, 593 602.

2. Wang F, et al. (2007) Mechanism of thioamide drug actionagainst tuberculosis and leprosy. J Exp Med 204, 73 8.

3. Fajardo T, et al. (2006) A clinical trial of ethionamide andprothionamide for treatment of lepromatous leprosy. AmJ Trop Med Hyg 74, 457 61.

4. Jenner P, et al. (1984) A comparison of the blood levelsand urinary excretion of ethionamide and prothionamidein man. J Antimicrob Chemother 13, 267 77.

5. www.promedgroup.com/prothionamide

PZA

Tuberculosis (2008) 88(2) 141–144

PyrazinamideGeneric and additional names: Pyrazinamide; pyrazinoic acid amide; pyrazine carboxyl-

amideCAS name: PyrazinecarboxamideCAS registry #: 98-96-4Molecular formula: C5H5N3OMolecular weight: 123.11Intellectual property rights: Generic, first synthesized in 1936

O

N

NNH2

Brand names: Pezetamid (Hefa-Frenon); Pyrafat (Fatol); Pirilene (Cassenne); Piraldina (Bracco); Tebrazid(Searle); Unipyranamide (Unichem); Zinamide (Merck & Co.)

Derivatives: Morphazinamide; pyrazinamide Mannich bases also active1

Solubility: Soluble in chloroform, methylene chloride; less soluble in benzene; sparingly soluble in water[Merck Index]

Polarity: Log P 1.884 [DrugBank]Melting point: 192ºC [DrugBank]Formulation and optimal human dosage: 500 mg tablets available.

Dose 20 25 mg/kg daily, or 50 70 mg/kg three times a week. Pyrazinamide is also available as part of fixed-dose combinations with other TB drugs such as isoniazid and rifampicin (Rifater® is an example).

Basic biology informationDrug target/mechanism: The mechanism of action ofpyrazinamide (PZA) is poorly understood: pyrazinoicacid (POA), the active moiety of PZA, has beenshown to inhibit various functions at acid pH in My-cobacterium tuberculosis.2,3 Experimental evidencesuggests that PZA diffuses into M. tuberculosis andis converted into POA by pyrazinamidase (PZAase);the in vitro susceptibility of a given strain of theorganism corresponds to its PZAase activity. PZAaseis also called nicotinamidase and metabolizes bothPZA and nicotinamide. Once converted, a portionof the POA exits the cell and, providing the mediapH is acidic, on protonation re-enters as protonatedPOA, which may help to disrupt membrane potential(reviewed in Zhang and Mitchison 20034). Aninefficient efflux system causes protonated POA todiffuse in at a faster rate than the efflux of POA.In fact, resperine an inhibitor of a multidrug-resistant efflux pump can sensitize the cells toPZA.3 The accumulation of POA and protonated POAlowers the intracellular pH to a suboptimal level thatmay inactivate many pathways including fatty acidsynthase and membrane transport function. Howeverit is widely accepted that POA may not have a specifictarget, but rather that cellular acidification causes

inhibition of major processes.4 Weak acids such asbenzoic acid, UV and respiratory chain inhibitors(e.g. sodium azide) enhance the action of PZA.5,6

Continuing studies on individual targets such asthe nicotinic acid pathway may lead to alternateproposals.Drug resistance mechanism: No target-specificmutants have been isolated to date. PZA-resistantmutations are usually found in the converting en-zyme PZAase.7 The mutations are unusually located,spread throughout the gene, but there are three ar-eas of clustered mutations around amino acids 3 71,61 85 and 132 142.8 A crystal structure of PZAaseis now available from Pyrococcus horikoshii and,although it only shares 37% identity with the M. tu-berculosis enzyme, it may help in understandingthe PZAase mutations in M. tuberculosis.9 LabeledPZA accumulates, probably as POA, inside sensitivebut not resistant M. tuberculosis, presumably be-cause of the lack of the converting enzyme (reviewedin Zhang and Mitchison 20034). A small number of PZAmutations occur outside the pncA gene (coding forPZAase) but these have not been characterized.8

In-vitro potency against MTB: MICs for M. tuberculo-sis are reported as 6 50mg/ml at pH 5.5 (reviewedin Zhang and Mitchison 20034) but >2000mg/ml


142 Pyrazinamide

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology


Guinea pig 5.3±0.6 185±6.5 23.8±2.1 Single oral dose 25 mg/kg19,20

Human 9.6±1.8 502±101 38.7±5.9 Single oral dose of 27±4 mg/kg17

for Escherichia coli and M. smegmatis at thesame pH. Careful monitoring is required duringMIC measurements as bacterial density and serumalbumin can affect results.4,10

Specifically, MIC90 at pH 5.5 is 50mg/ml, at pH 5.8 is100mg/ml, at pH 5.95 is 200mg/ml.10

Spectrum of activity: PZA is presumed to be specificfor Mycobacterium species, exerting its antibacterialproperties under specific conditions (acidic pH).M. bovis and M. leprae are innately resistant toPZA. PZAase is widely distributed in bacteria yetefficacy of PZA is limited to M. tuberculosis and fewother organisms. All bovine mycobacterial strainslack PZase activity due to a point mutation inthe pncA gene. M. smegmatis is also PZA resistantprobably due to a very efficient efflux system whichdoes not allow POA to accumulate within the cell.4

Other in-vitro activity: Anaerobic conditions en-hanced the activity of PZA.5 Older cultures of M. tu-berculosis appear to be somewhat more sensitiveto PZA11 and have a weaker membrane potentialcompared to fresh cultures.3 Under some conditionsbactericidal activity is inversely proportional to[3H]uridine uptake, reflecting the activity of PZAagainst persistent bacilli in vivo.11 An elegantexperiment showed PZA activity against E. colipersistors following treatment with ampicillin.6

PZA activity against M. tuberculosis in macrophagesis controversial12 although many authors do reportsome activity.4 PZA has been shown to be effectivein whole blood assays13 where blood harvested froma drug-treated donor was used as a medium in whichto grow the bacilli.In-vivo efficacy in animal model: PZA has little in-vivo activity over the first few days but has activityagainst persistors late in the course of infection;this drug has greater activity against slow-growingorganisms as compared with its activity againstactively replicating forms (reviewed in Zhang andMitchison 20034). Regimens with PZA have betterlong-term outcomes in terms of organ sterilitycompared with those without PZA (reviewed inGrosset et al. 199214). In a series of criticalobservations when mice were dosed with rifampin(RIF) and PZA together (but not separately) no bacillicould be detected after 12 weeks of therapy,15

however 12 weeks after treatment cessation bacillicould be detected in some animals.16 This model,now called the Cornell model of TB infection,provides a method to determine the effect ofcompounds on dormant bacilli.As a single agent in mice, PZA (i.v. infection, drugadministered at 150 mg/kg 6 times/week, beginning14 days post infection) was slightly less effectivecompared to isoniazid (INH) at 2, 4 and 8 weeks,about equivalent with RIF at 2 and 4 weeks but lesseffective by 8 weeks.17

Efficacy in humansPZA is generally used in combination with otherdrugs such as INH and RIF in the treatment ofMycobacterium tuberculosis. Treatment regime mostoften used: initially INH, RIF, PZA, ETH dailyfor 2 months followed by INH and RIF 3 timesweekly for 4 months [DrugBank]. Specific dosesand specific treatment times vary and detailscan be found in many sources including Centersfor Disease Control [http://www.cdc.gov/mmwR/preview/mmwrhtml/rr5211a1.htm] and the WorldHealth Organization [http://www.who.int/en/]. PZAshortens therapy from ~11 months to ~6 months bykilling organisms not affected by other TB drugs,especially those in acidic environments. PZA usedin the first two months of treatment reducesthe duration of treatment required, PZA alsoreduced the relapse rate from 22% to 8% whenadded to a combination with INH and streptomycin(STR) (reviewed in Zhang and Mitchison 20034 andMitchison 200018). It crosses inflamed meninges andis an essential part of the treatment of tuberculosismeningitis.

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Guinea pig: Bioavailability 92%.• Human: Protein binding is 10 20%. PZA is rapidly

and well absorbed from the gastrointestinal tract.It crosses the meninges.

Human metabolic pathway: Metabolized in the liverby a microsomal deamidase to POA, the metabolicproducts are excreted by the kidneys. PZA is widely

PZA

Pyrazinamide 143

distributed to most fluids and tissues, includingliver, lungs, kidneys, and bile. PZA has excellentpenetration into CSF, ranging from 87% to 105% ofthe corresponding serum concentration.

Safety and TolerabilityAnimal drug drug interactions: Antagonism occursbetween INH, RIF and PZA in mice (see INH articlefor details).14

Animal toxicity: Guinea pigs receiving daily oraldoses of 25 mg/kg PZA for 8 weeks were evaluatedfor hepatotoxicity 7 days after final dose; ALTlevels in serum: control animals 45.2±1.2 U/ml, PZA-treated animals 152±39.5 U/ml, animals treatedwith PZA in an alginate formula 46.5±5.7 U/ml.Hepatotoxicity, evident after 8 weeks of drugtreatment, was reversed with alginate formulationwhich did not affect efficacy.21 It is worth noting thata review indicates PZA does not work well against TBin guinea pig models.4 Similar changes were seen inrats given 35 mg/kg oral PZA with INH and RIF for45 days, toxicity being somewhat reversed by theaddition of specific plant extracts.22

Carcinogenicity: In lifetime bioassays in rats andmice, PZA was administered in the diet atconcentrations of up to 10,000 ppm. This resulted inestimated daily doses for the mouse of 2 g/kg, or40 times the maximum human dose, and for the ratof 0.5 g/kg, or 10 times the maximum human dose.PZA was not carcinogenic in rats or male mice andno conclusion was possible for female mice due toinsufficient numbers of surviving control mice.PZA was not mutagenic in the Ames bacterial test,but induced chromosomal aberrations in humanlymphocyte cell cultures.Animal safety pharmacology: No systemic adverseeffects were found, except equivocal findingsrelating to fetal weight, when PZA was administeredto mice at 8× therapeutic dose (1200 mg/kg, orally)giving a Cmax 9 12× that of the therapeutic dose.23

Human drug drug interactions: Due to potential forliver toxicity alcohol intake should be limited duringPZA treatment. PZA may decrease the effects ofallopurinol (Zyloprim). PZA has been reported tointerfere with ACETEST® and KETOSTIX® urine teststo produce a pink-brown color [DrugBank].Human potential toxicity: Hepatitis: The principaladverse effect is a hepatic reaction. Hepatotoxicityappears to be dose related, and may appear at anytime during therapy. Gastrointestinal disturbancesincluding nausea, vomiting and anorexia have alsobeen reported [DrugBank].At 40 50 mg/kg daily ~15% of individuals showliver toxicity effects, however at the currentlyrecommended dose of 15 30 mg/kg daily the hepato-toxicity risk decreases significantly. Other common

side effects can include gastrointestinal distresswhich often abates on further dosing, and increasesin serum uric acid. The latter is observed as POAcompetes with uric acid for renal filtration; uric acidlevels and accompanying polyarthralgia decreasewhen drug is administered 2 or 3 times a week.24

PZA should not be used to treat latent tuberculosisbecause the rate of liver toxicity is unacceptablyhigh.Human adverse reactions:Side effects include liver injury, arthralgias,anorexia, nausea and vomiting, dysuria, malaise andfever, sideroblastic anaemia.Adverse effects on the blood clotting mechanismor vascular integrity, and hypersensitivity reactionssuch as urticaria, pruritis and skin rashes may occur.PZA is contraindicated in persons with severe liverdamage or with acute gout.PZA should be discontinued and not be resumedif signs of hepatocellular damage or hyperuricemiaaccompanied by an acute gouty arthritis appear[DrugBank].

References1. Sriram D, et al. (2006) Synthesis of pyrazinamide Mannich

bases and its antitubercular properties. Bioorg Med ChemLett 16, 2113 6.

2. Boshoff H, et al. (2002) Effects of pyrazinamide on fattyacid synthesis by whole mycobacterial cells and purifiedfatty acid synthase I. J Bacteriol 184, 2167 72.

3. Zhang Y, et al. (2003) Mode of action of pyrazinamide:disruption of Mycobacterium tuberculosis membranetransport and energetics by pyrazinoic acid. J AntimicrobChemother 52, 790 5.

4. Zhang Y, Mitchison D (2003) The curious characteristics ofpyrazinamide: a review. Int J Tuberc Lung Dis 7, 6 21.

5. Wade M, Zhang Y (2004) Anaerobic incubation conditionsenhance pyrazinamide activity against Mycobacteriumtuberculosis. J Med Microbiol 53, 769 73.

6. Wade M, Zhang Y (2006) Effects of weak acids, UV andproton motive force inhibitors on pyrazinamide activityagainst Mycobacterium tuberculosis in vitro. J AntimicrobChemother 58, 936 41.

7. Davies A, et al. (2000) Comparison of phenotypic andgenotypic methods for pyrazinamide susceptibility. J ClinMicrobiol 38, 3686 8.

8. Scorpio A, et al. (1997) Characterization of pncA mutationsin pyrazinamide-resistant Mycobacterium tuberculosis.Antimicrob Agents Chemother 41, 540 3.

9. Du X, et al. 2001, Crystal structure and mechanism ofcatalysis of a pyrazinamidase from Pyrococcus horikoshii.Biochemistry 40, 14166 72.

10. Salfinger M, Heifets L (1988) Determination ofpyrazinamide MICs for Mycobacterium tuberculosis atdifferent pHs by the radiometric method. AntimicrobAgents Chemother 32, 1002 4.

11. Hu Y, et al. (2006) Sterilising action of pyrazinamide inmodels of dormant MTB. Int J Tuberc Lung Dis 10, 317 22.

12. Teyssier L (2001) Higher activity of morphazinamideover pyrazinamide against intracellular Mycobacteriumtuberculosis. Int J Tuberc Lung Dis 5, 386 98.

144 Pyrazinamide

13. Wallis R, et al. (2001) A whole blood bactericidal assay fortuberculosis. J Infect. Dis 83, 1300 3.

14. Grosset J, et al. (1992) Antagonism between isoniazidand the combination pyrazinamide rifampin againsttuberculosis infection in mice. Antimicrob AgentsChemother 36, 548 51.

15. McCune R, Thompsett R (1956) Fate of Mycobacteriumtuberculosis in mouse tissues as determined by themicrobial enumeration technique. I. The persistence ofdrug-susceptible tubercle bacilli in the tissues despiteprolonged antimicrobial therapy. J Exp Med 104, 737 62.

16. McCune R, et al. (1956) The fate of Mycobacteriumtuberculosis in mouse tissues as determined by themicrobial enumeration technique. II. The conversionof tuberculous infection to the latent state by theadministration of pyrazinamide and a companion drug.J Exp Med 104, 763 802.


18. Mitchison D (2000) Role of individual drugs in thechemotherapy of tuberculosis. Int J Tuberc Lung Dis 4,796 806.

19. Pandey R, et al. (2003) Poly(dl-lactide-co-glycolide)nanoparticle-based inhalable sustained drug deliverysystem for experimental tuberculosis. J AntimicrobChemother 52, 981 6.


21. Qurrat-ul-Ain et al. (2003) Alginate-based oral drugdelivery system for tuberculosis: pharmacokinetics andtherapeutic effects. J Antimicrob Chemother 51, 931 8.

22. Pari L, Kumar N (2002) Hepatoprotective activity ofMoringa oleifera on antitubercular drug-induced liverdamage in rats. J Med Food 5, 171 7.

23. NIH (1997) NIEHS AIDS Therapeutics Toxicity ReportNumber 1, NIEHS Technical Report on the Reproductive,Developmental, and General Toxicity Studies of Pyrazin-amide Administered by Gavage to Swiss (CD-1®) Mice.NIH Publication 97 3938, 1997, United States Departmentof Health and Human Services, Public Health Service,National Institutes of Health.


RIFAB

Tuberculosis (2008) 88(2) 145–147

RifabutinGeneric and additional names: RifabutinCAS name: 1′,4-didehydro-1-deoxy-1,4-dihydro-5′-(2-methylpropyl)-

1-oxorifamycin XIVCAS registry #: 72559-06-9Molecular formula: C46H62N4O11Molecular weight: 847.005Intellectual property rights: GenericBrand names: Ansamycin, Alfacid, Ansatipin, Ansatipine, Antibiotic

LM 427, Mycobutin, RBTDerivatives: KRM-1648 (also called Rifalazil or ABI-1648),

rifapentineSolubility: Rifabutin is a red-violet powder soluble in chloroform and

methanol, sparingly soluble in ethanol, and very slightly soluble inwater [Merck Index]. Water solubility is 0.19 mg/ml [DrugBank]

Polarity: Log P 4.218 [DrugBank]

O

OO

MeOMe

HO

OMe

Me

O

Me

OHOH

Me

Me

NH

OMeO

N

Me

NH

N

Me

Me

Formulation and optimal human dosage: Rifabutin is a spiro-piperidyl-rifamycin derived from rifamycin-S.Dose 300 mg 1× daily, Capsules 150 mg, Pharmacia

Basic biology informationDrug target/mechanism: See rifampin (RIF).Drug resistance mechanism: As with RIF, most ofthe clinical Mycobacterium tuberculosis mutationsresulting in resistance to rifabutin (RIFAB) are in therpoB gene, generally confined to the RIF-resistancedetermining region (RDR). Some mutations conferresistance to all the rifamycin analogs whereasothers were found to be specific to RIF andrifapentine (RIFAP) but not to KRM-1648 (RIFAL)or RIFAB.1 A significant number of publications onthese mutations can be found1 3 and most ofthe authors agree that both position and typeof substitution play a role in sensitivity to therifamycins; as a general rule, mutations at codons511 and 516 result in resistance to RIF andRIFAP but sensitivity to RIFAL and RIFAB, whilemutations at codon 531 result in high-level resistanceto all the rifamycin analogs. A few rifamycin-resistant mutations are found outside the RDR;in Escherichia coli there are some mutationalhot spots outside the core region of rpoB whichresult in rifamycin resistance, and the same mayapply in M. tuberculosis. No rifamycin-resistantM. tuberculosis mutations outside rpoB have beenmapped, but mutations outside the RDR or alteration

in drug transporters or membrane permeability aresuspected in these cases.2

In-vitro potency against MTB: M. tuberculosis H37RvMICs: RIFAP 0.031mg/ml, RIFAB <0.015mg/ml, RIF0.25mg/ml.1

Spectrum of activity: RIFAB and RIFAP are activeagainst the same spectrum of mycobacteria as RIFalthough differences in absolute MICs have beenidentified. RIFAB and RIFAP are more active thanRIF in vitro against the M. avium complex (MAC),M. tuberculosis, and M. leprae.4,5

Other in-vitro activity: RIFAB MICs: M. africanumATCC 25420 0.063mg/ml, M. bovis ATCC 192100.125mg/ml.6 MICs for other strains are provided inthe same paper.6

Activity against M. avium: RIFAB 0.06mg/ml; RIFAP0.125mg/ml.7

Greater efficacy was seen against Toxoplasma gondiiin vitro, with RIFAP being better than RIFAB in vitro,but atovaquone, a known T. gondii treatment,outperformed them both. No host-cell toxicity wasobserved at efficacious levels of 10mg/ml. RIFAPand RIFAB were active in vivo in a mouse model,where they showed superior activity to atovaquoneat 50 mg/kg but inferior activity at 100 mg/kg. AgainRIFAP outperformed RIFAB at both levels.8


146 Rifabutin

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Human 45±17(range 16 69)

375±267ng/ml

0.69±0.32l/h/kg

300 mg single oral dose to healthyvolunteers [FDA label]

In-vivo efficacy in animal model: The antimicrobialactivities of RIF, RIFAB and RIFAP were comparedin BCG-vaccinated and M. tuberculosis-infectedimmunocompetent mice. Using an equal weightbasis both RIFAP and RIFAB were more bactericidalthan RIF. The activity of RIF was significantlyreduced when drug was administered to micethree times a week instead of six times a week,however significant bactericidal activity was stillobserved in mice treated with RIFAP, 10 mg/kg upto once every two weeks, or RIFAB, 10 mg/kg twiceweekly. The bactericidal activity of RIFAB, 10 mg/kgsix times/week for 6 weeks, or RIFAP, 10 mg/kgtwice/week for 12 week, was comparable to that ofRIF, 10 mg/kg six times/week for 12 weeks in mice.9

Pharmacokinetic experiments comparing RIF, RIFABand RIFAP demonstrated that RIFAP had the highestserum peak level (Cmax) and the longest half-life,whereas RIFAB displayed the lowest Cmax and theshortest half-life.9

In vivo (mouse) against M. avium RIFAB showedbetter activity than RIF and slightly better activitythan RIFAP.7 See also the In vivo efficacy section forRIFAP.

Efficacy in humansRIFAB is significantly more lipid soluble than is RIF,resulting in higher tissue uptake, a larger volume ofdistribution, lower maximum plasma concentrations,lower trough concentrations, a longer terminal half-life, and higher tissue-to-plasma drug concentrationratios. RIFAB is recommended for HIV patientsbecause it induces microsomal enzymes significantlyless than RIF and has the potential to havea reduced effect on the serum concentrationsof protease inhibitors.10 One risk/benefit studyreported an increase in AUC for RIFAB (RIFAB 300 mg2× weekly, Nelfinavir 1250 mg 2× daily) and itsmetabolite deacetyl-RIFAB with patients receivingNelfinavir; however the drug levels were still withinacceptable limits. The data confirm the provisionalCDC guideline that dosage adjustment is unnecessarywhen 600 mg doses of RIFAB are administered twiceweekly with Nelfinavir. The effect on Nelfinavir levelswas negligible.11 However other studies have shownthe development of RIF-resistant organisms withRIFAB in HIV patients due to a decrease in RIFAB

AUC levels for patients with low CD4 counts.12,13

Burman et al.14 note that both RIFAB and RIFAPexhibit idiosyncratic clinical efficacy; RIFAB is activedespite unfavorable Cmax/MIC ratios while RIFAPexhibits sub-optimal clinical performance despite avery favorable Cmax/MIC ratio. These phenomenamay be partly explained by differences in proteinbinding and in intracellular penetration.14

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Human: Lung:plasma ratio is 6.5 [FDA label].

Average bioavailability is 20% but this maydecrease with multiple doses [FDA label, Goodman& Gilman’s}]. RIFAB is 71% protein bound; ratioof extracellular to intracellular concentration is3.5 for RIFAB and 5 for RIF.14 Repeated doses donot appear to affect clearance of RIFAP but doaffect clearance of RIF and RIFAB; with repeateddoses the AUC of RIFAB is lowered but the half-lifeis unaffected. Steady-state levels of RIF and RIFABare achieved after 6 days of daily dosing (reviewedin Burman et al. 200114).

Animal metabolic pathway: In a comprehensivepublication15 on RIFAB metabolism in rats, rabbits,monkeys and man 31-hydroxy-RIFAB was detected asthe major metabolite in the plasma of all speciesbetween 8 and 24 hours post dosing; 25-deacetyl-RIFAB was only found in rats and man. The excretionroute for RIFAB is renal and fecal; trace amountsare excreted as the parent compound in the urineof rabbits and monkeys, whereas these amounts are8.5% and 4.6% in rat and man, respectively.15

Human metabolic pathway: 5 10% of RIFAB is ex-creted unchanged in the urine compared with 13 24%of RIF.14 53% of total dose was excreted in urine asparent or metabolites and 30% in faeces [DrugBank].Plasma elimination half-life is 32 67 hours.14 RIFABis metabolized to at least 20 components, 7 of whichhave been identified in human urine; these include25-O-deacetyl-RIFAB, 30-hydroxy-RIFAB, 31-hydroxy-RIFAB, 32-hydroxy-RIFAB, 32-hydroxy-25-O-deacetyl-RIFAB and 25-O-deacetyl-RIFAB-N-oxide.14

Safety and TolerabilityAnimal toxicity: Liver abnormalities (increasedbilirubin and liver weight), occurred in all species

RIFAB

Rifabutin 147

tested, in rats at doses 5 times, in monkeys atdoses 8 times, and in mice at doses 6 timesthe recommended human daily dose. Testicularatrophy occurred in baboons at doses 4 timesthe recommended human dose, and in rats atdoses 40 times the recommended human daily dose[FDA label].Human drug drug interactions: In general therifamycins do induce CYP3A in gut and liver butnot in neutrophils and lymphocytes. The relativeinduction of CYP3A by the rifamycins is RIF >RIFAP > RIFAB, although this is generally reversed 1 2weeks following drug cessation (reviewed in Burmanet al. 200114). Other microsomal enzymes arealso affected, namely CYP1A2, CYP2C and CYP2D6.Rifamycins in general should not be given with azoleantifungals as subtherapeutic serum concentrationsof the latter can result (reviewed in Burmanet al. 200114), although the FDA label indicates adecrease in the drug levels of itraconazole, but notfluconazole, when given with RIFAB.Human potential toxicity: RIFAB may rarely beassociated with myositis and uveitis; the uveitisincidence did increase with increasing RIFAB dose[FDA label]. Diarrhoea, fever, heartburn, indigestion,loss of appetite, nausea, skin itching and/or rashhave all been associated with RIFAB treatment. The“flu-like” symptoms associated with RIF treatmentalso occur in patients taking RIFAB.16 Thrombocy-topenia has also been linked to RIFAB [FDA label].Human adverse reactions: Hepatitis frequency issimilar to that seen with RIF, and probably notassociated with the rifamycins alone but with thesedrugs in combinations with other TB treatments.14

Cardiovascular: similar to RIF.Respiratory: similar to RIF.CNS: similar to RIF.Gastrointestinal: similar events and frequency withRIF, RIFAB and RIFAP (nausea, vomiting, diarrhoea).Uveitis, corneal deposits, neutropenia, arthralgiasand skin discoloration have all been associated withRIFAB treatment; these symptoms were exacerbatedwith high RIFAB (>600 mg/day) and with RIFABand other CYP3A inhibitors such as clarithromycin.Dose reductions ablated these findings (reviewed inBurman et al. 200114).

References1. Williams D, et al. (1998) Contribution of rpoB mutations

to development of rifamycin cross-resistance in Mycobac-

terium tuberculosis. Antimicrob Agents Chemother 42,1853 7.

2. Yang B, et al. (1998) Relationship between antimy-cobacterial activities of rifampicin, rifabutin and KRM-1648 and rpoB mutations of Mycobacterium tuberculosis.J Antimicrob Chemother 42, 621 8.

3. Saribas Z, et al. (2003) Rapid detection of rifampinresistance in Mycobacterium tuberculosis isolates byheteroduplex analysis and determination of rifamycincross-resistance in rifampin-resistant isolates. J ClinMicrobiol 41, 816 8.

4. Kunin C, et al. (1996) Antimicrobial activity of rifabutin.Clin Infect Dis 22(Suppl 1), S3 13. Discussion: S13 4.

5. Bemer-Melchior P, et al. (2000) Comparison of thein vitro activities of rifapentine and rifampicin againstMycobacterium tuberculosis complex. J AntimicrobChemother 46, 571 6.

6. Rastogi N, et al. (2000) Activity of rifapentineand its metabolite 25-O-desacetylrifapentine comparedwith rifampicin and rifabutin against Mycobacteriumtuberculosis, Mycobacterium africanum, Mycobacteriumbovis and M. bovis BCG. J Antimicrob Chemother 46,565 70.

7. Klemens S, et al. (1991) In vivo activities of newerrifamycin analogs against M. avium infection. AntimicrobAgents Chemother 35, 2026 30.

8. Araujo F, et al. (1996) Rifapentine is active in vitroand in vivo against Toxoplasma gondii. Antimicrob AgentsChemother 40, 1335 7.

9. Ji B, et al. (1993) Effectiveness of rifampin, rifabutin,and rifapentine for preventive therapy of tuberculosis inmice. Am Rev Respir Dis 148, 1541 6.

10. Centers for Disease Control and Prevention (2000) Updatedguidelines for the use of rifabutin or rifampin forthe treatment and prevention of tuberculosis amongHIV-infected patients taking protease inhibitors ornonnucleoside reverse transcriptase inhibitors. MMWRMorb Mortal Wkly Rep 49(9), 185 9. Available on-line atwww.cdc.gov/nchstp/tb/

11. Benator D, et al. (2007) Clinical evaluation ofthe nelfinavir rifabutin interaction in patients withtuberculosis and human immunodeficiency virus infection.Pharmacotherapy 27, 793 800.

12. Weiner M, et al. (2005) Association between acquiredrifamycin resistance and the pharmacokinetics of rifabutinand isoniazid among patients with HIV and tuberculosis.Clin Infect Dis 40, 1481 91.

13. Burman W, et al. (2006) Acquired rifamycin resistance withtwice-weekly treatment of HIV-related tuberculosis. Am JRespir Crit Care Med 173, 350 6.

14. Burman W, et al. (2001) Comparative pharmacokineticsand pharmacodynamics of the rifamycin antibacterials.Clin Pharmacokinet 40, 327 41.

15. Battaglia R, et al. (1990) Absorption, disposition andpreliminary metabolic pathway of 14C-rifabutin in animalsand man. J Antimicrob Chemother 26, 813 22.

16. Matteelli A, et al. (2005) Tolerability of twice-weeklyrifabutin isoniazid combinations versus daily isoniazid forlatent tuberculosis in HIV-infected subjects: a pilot study.Int J Tuberc Lung Dis 3, 1043 6.

Tuberculosis (2008) 88(2) 148–150

RifalazilGeneric and additional names: Rifalazil (also known as

KRM-1648 or ABI-1648)CAS name: 3′-Hydroxy-5′-(4-isobutylpiperazinyl)benzoxy-

azinorifamycinCAS registry #: 129791-92-0Molecular formula: C51H64N4O13Molecular weight: 941.08Intellectual property rights: Kaneka CorpDerivatives: Rifampin; Rifapentine; Rifabutin.Solubility: Rifalazil (or KRM-1648) has a relatively high

water solubility of more than 2000 mg/ml at pH 2 anda low solubility of less than 0.1 mg/ml at greater thanpH 5.1

O

OO

MeOMe

HO

OMe

Me

O

Me

OHOH

Me

Me

NH

OMeO

N

Me

O

HO N

NMe

Me

Basic biology informationDrug target/mechanism: See Rifampin (RIF)Drug resistance mechanism: As with all rifamycins,most of the clinical Mycobacterium tuberculosismutations resulting in resistance to rifapentine(RIFAP) and rifalazil (RIFAL) are in the rpoB gene,generally confined to the RIF-resistance determiningregion (RDR). Some mutations confer resistanceto all the rifamycin analogs whereas others werefound to be specific to rifampin (RIF) and RIFAPbut not to RIFAL or rifabutin (RIFAB).2 A significantnumber of publications on these mutations can befound,2,3 and most of the authors agree that bothposition and type of substitution play a role insensitivity to the rifamycins; as a general rule,mutations at codons 511 and 516 result in resistanceto RIF and RIFAP but sensitivity to RIFAL and RIFAB;mutations at codon 531 result in high-level resistanceto all the rifamycin analogs. A 1996 publicationwhich examined 24 RIF-resistant isolates showedthat RIFAL was better at overcoming this resistancethan RIFAP.4 A few rifamycin-resistant mutations arefound outside the RDR; in Escherichia coli there aresome mutational hot spots outside the core regionof rpoB which result in rifamycin resistance, and thesame may apply in M. tuberculosis. No RIF-resistantM. tuberculosis mutations outside rpoB have beenmapped, but alteration outside the RDR or in drugtransporter or membrane permeability is suspectedin these cases.3

In-vitro potency against MTB: M. tuberculosis H37RvMICs: RIFAP 0.031mg/ml, RIFAB <0.015mg/ml, RIF0.25mg/ml, RIFAL (listed as KRM-1648) <0.015mg/ml.2

Other authors note that RIFAL has 64-fold lower MICagainst M. tuberculosis compared with RIF, and is4 8-fold more active compared with RIFAB (reviewedin Dietze et al. 20015).Spectrum of activity: RIFAL is active against manyof the mycobacteria with a similar spectrum to theother rifamycins; it has superior activity againstseveral species compared with RIF.6 Outside themycobacteria RIFAL has a similar spectum as RIF,RIFAP and RIFAB.Other in-vitro activity: RIFAL has excellent cellpenetration possibly because it is more lipophilicthan RIF,3 it has similar activity against the isolatedtarget (reviewed in Tomioka 20007). Yang3 ranks therifamycins in the following order of decreasing MIC:RIF > RIFAP> RIFAL. Activity has been demonstratedin vitro for M. kansasii, M. marinum, M. scrofu-laceum, M. avium, M. fortuitum, M. intracellulareand M. chelonae.6 RIFAL is active against M. tuber-culosis and M. intracellulare in macrophages withactivity equal to RIFAP but superior to RIF.6 RIFALdemonstrated activity against the M. avium complex(MAC) that was superior to clarithromycin; potentia-tion was observed in combination with ethambutol.RIFAL has exceptional activity against Chlamydiatrachomatis; MIC for RIF is 0.004mg/ml, for RIFAL0.00025mg/ml.8


RIFAL

Rifalazil 149

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Rat 15.6 6.1 0.16 0.64 l/h/kg 30 mg/kg oral dose1

Human 8.7±2.7 852.1±407.1ng·h/ml

24.5±14.7ng/ml

The half-life data reported here5

were obtained following the firstRIFAL dose with 25 mg oral drug.The AUC and Cmax data are for asingle 25 mg oral dose in malefasted volunteers.15

In-vivo efficacy in animal model: RIFAL, similar toRIFAB but unlike RIF, has high tissue levels but lowplasma levels in mice. RIFAL had a better therapeuticwindow against M. tuberculosis in mice comparedwith RIFAB and RIFAP and was active against somemoderately RIF-resistant strains. RIFAL also hadbetter activity against MAC in mice compared to theother rifamycins (reviewed in Tomioka et al. 19929

and Tomioka 20007).Long-term treatment of M. tuberculosis-infectedmice to determine the conditions (comparing RIFAL20 mg/kg, INH 25 mg/kg +/ PZA 150 mg/kg) underwhich RIFAL treatment would result in sterilizationshowed that although all animals were negative at10 weeks, 2 3 of 8 mice relapsed three months aftertreatment.10

Success with RIFAL in the treatment of otherbacterial diseases, for example Clostridium difficileand Chlamydia, has been reported (Anton et al.2004;11 reviewed in Suchland et al. 200612).

Efficacy in humansIn a randomized open-label phase-2 clinical trialRIFAL was used in the first 2 weeks of treatmentwith smear-positive patients. RIFAL was administeredonce weekly at 10 or 25 mg with isoniazid 5 mg/kgdaily. Adverse events with RIFAL were the sameas with other treatments used in the studyalthough statistically insignificant increases in flu-like symptoms were observed at the high RIFAL dose;transient decreases in absolute neutrophil countswere noted in 10 20% of the RIFAL patients. Dueto issues with the control no conclusions could bedrawn as to drug efficacy in this study (Dietze et al.2001;5 http://www.case.edu/affil/tbru/trials.htm].No drug-resistant organisms were seen. No furtherM. tuberculosis clinical trials have been reported.De Souza13 reports severe side effects in a clinicaltrial of RIFAL but provides no reference.ActivBiotics has reported a phase-2/3 RIFAL trial inpatients with peripheral arterial disease and highantibody titers to Chlamydia pneumoniae. The trialdid not show the expected improvement in heart-

disease symtoms although no specific reference wasmade to the microbiological outcome of the trial.14

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Mouse: PK data have been published but are not

readily accessible.16

• Rat: PK data for a variety of doses have beenreported by Hosoe et al.1 Bioavailability for 3, 30and 100 mg/kg doses was 26.9%, 13% and 4.7%,respectively. Protein binding ~99.5%.1

• Dog: Protein binding 99.8%.1 PK data for a varietyof doses have been reported by Hosoe et al.1

Bioavailability for 3, 30 and 100 mg/kg doses was42.9%, 21.0% and 8.0%, respectively.1

• Human: Half-life 61 hours, Cmax 44 ng/ml (at-tributed to Rose et al. 1999 in review by Dietzeet al.5). RIFAL may not be absorbed as well byTB patients as by uninfected controls.5

RIFAL was safe and well tolerated under fed andfasting conditions when given at a single doseof 25 mg/mg.15 RIFAL reaches high intracellularconcentrations and has excellent tissue penetra-tion.17

Animal metabolic pathway: Two major metabolitesof RIFAL were identified from mouse urine; one was25-deacetyl rifalazil, the other was probably 32-hydroxy rifalazil. Both metabolites were also ob-tained following incubation of the parent drug withpooled human liver microsomes. The antimicrobialactivities of the metabolites were similar to that ofthe parent drug.18

Safety and TolerabilityAnimal drug drug interactions: RIFAL does notinduce P450 enzymes and is not metabolized by theseenzymes1 thus the drug drug interactions may beless compared with the other rifamycins (reviewedin Dietze et al. 20015).Human adverse reactions: In clinical trials 10 mg and25 mg once weekly doses of RIFAL were generallywell tolerated; dose-related flu-like symptoms were

150 Rifalazil

observed similar as seen with RIF; other observationsincluded a transient decrease in blood countsincluding platelets, white cells and absolute neu-trophil numbers; similar numbers were seen in theRIF arm.5

References1. Hosoe K, et al. (1996) Pharmacokinetics of KRM-1648, a

new benzoxazinorifamycin, in rats and dogs. AntimicrobAgents Chemother 40, 2749 55.

2. Williams D, et al. (1998) Contribution of rpoB mutationsto development of rifamycin cross-resistance in Mycobac-terium tuberculosis. Antimicrob Agents Chemother 42,1853 7.


4. Moghazeh S, et al. (1996) Comparative antimycobacterialactivities of rifampin, rifapentine, and KRM-1648against a collection of rifampin-resistant Mycobacteriumtuberculosis isolates with known rpoB mutations.Antimicrob Agents Chemother 40, 2655 7.

5. Dietze R, et al. (2001) Safety and bactericidal activityof rifalazil in patients with pulmonary tuberculosis.Antimicrob Agents Chemother 45, 1972 6.

6. Saito H, et al. (1991) In vitro antimycobacterial activitiesof newly synthesized benzoxazinorifamycins. AntimicrobAgents Chemother 35, 542 7.

7. Tomioka H (2000) Prospects for development of newantimycobacterial drugs. J Infect Chemother 6, 8 20.

8. Xia M, et al. (2005) Activities of rifamycin derivativesagainst wild-type and rpoB mutants of Chlamydiatrachomatis. Antimicrob Agents Chemother 49, 3974 6.

9. Tomioka H, et al. (1992) Chemotherapeutic efficacy ofa newly synthesized benzoxazinorifamycin, KRM-1648,against Mycobacterium avium complex infection inducedin mice. Antimicrob Agents Chemother 36, 387 93.

10. Shoen C, et al. (2000) Evaluation of rifalazil in long-termtreatment regimens for tuberculosis in mice. AntimicrobAgents Chemother 44, 3167 8.

11. Anton P, et al. (2004) Rifalazil treats and prevents relapseof Clostridium difficile-associated diarrhea in hamsters.Antimicrob Agents Chemother 48, 3975 9.

12. Suchland R, et al. (2006) Rifalazil pretreatment ofmammalian cell cultures prevents subsequent Chlamydiainfection. Antimicrob Agents Chemother 50, 439 44.

13. de Souza M (2006) Promising drugs against tuberculosis.Recent Patents Anti-Infect Drug Discov 1, 33 44.

14. http://www.activbiotics.com/companyNews/index.html15. Chen Y, et al. (2007) Effect of food on the

pharmacokinetics of rifalazil, a novel antibacterial, inhealthy male volunteers. J Clin Pharmacol 47, 841 9.

16. Yamane T, et al. (1993) Synthesis and biological activityof 3′-hydroxy-5′-aminobenzoxazinorifamycin derivatives.Chem Pharm Bull Tokyo 41, 148 55.

17. Rothstein D, et al. (2006) Development potential ofrifalazil and other benzoxazinorifamycins. Expert OpinInvest Drugs 15, 3 23.

18. Mae T, et al. (1999) Isolation and identification of majormetabolites of rifalazil in mouse and human. Xenobiotica29, 1073 87.

RIF

Tuberculosis (2008) 88(2) 151–154

RifampinGeneric and additional names: 5,6,9,17,19,21-hexahydroxy-

23-methoxy-2,4,12,16,18,20,22-heptamethyl-8-[N-(4-methyl-1-piperazinyl)formimidoyl]-2,7-(epoxypentadeca[1,11,13]trienimino)naphtho[2,1-b]furan-1,11(2H)-dione 21-acetate; rifampicin; rifaldazine;rifamycin AMP; R/AMP

CAS name: 3-{[(4-Methyl-1-piperazinyl)imino]methyl}rifamycinCAS registry #: 13292-46-1Molecular formula: C43H58N4O12Molecular weight: 822.94Intellectual property rights: Generic. Parent compound

originally identified as a natural product from Amycolatopsisat Lapetit, Milan, Italy.1 Lapetit collaborated with Ciba-Geigyin the early development of this compound.1

O

OO

MeOMe

HO

OMe

Me

O

Me

OHOH

Me

Me

NH

OMeOH

OH

Me

NN

NMe

Brand names: Rifampin, rifampicin, rifamycin. Abrifam (Abbott); Eremfat (Fatol); Rifa (Grunenthal);Rifadin(e), Rifaldin (Aventis); Rifapiam (Piam); Rifaprodin (Almirall); Rifoldin (Aventis); Rimactan(e)(Novartis)

Derivatives: Rifapentine, rifalazil, rifabutinSolubility: Freely soluble in chloroform and DMSO; soluble in ethyl acetate, methanol, tetrahydrofuran; slightly

soluble in acetone, water, carbon tetrachloride [Merck Index]Polarity: Log P 3.719 [DrugBank]Acidity/basicity: pKa 1.7 for the 4-hydroxy and pKa 7.9 for the 3-piperazine nitrogen [Merck Index]Stability: Very stable in DMSO; rather stable in water [Merck Index].Melting point: 183ºC [DrugBank]Formulation and optimal human dosage: 300 mg tablets (Mycobution, Upjohn). Dose 10 mg/kg, in a single daily

administration, not to exceed 600 mg/day, oral or i.v.Rifampin is also available as part of fixed-dose combinations with other TB drugs such as isoniazid andpyrazinamide (Rifater® is an example).

Basic biology informationDrug target/mechanism: Rifampin (RIF) inhibits theessential rpoB gene product b-subunit of DNA-dependent RNA polymerase activity, acting early intranscription.2 It is thought to bind to the b subunit,close to the RNA/DNA channel, and physically blocksthe transit of the growing RNA chain after 2 3nucleotides have been added. In Escherichia colibactericidal action may come from the triggering ofapoptosis via activation of the “suicide gene module”mazEF, and the same system has been identified inMycobacterium tuberculosis.3 RIF does not inhibitthe mammalian enzyme.Drug resistance mechanism: >97% of mutants occurin RIF-resistant determining region (RDR), a 81 bp

stretch of the rpoB gene. Both clinical and laboratoryderived mutants are seen around amino acids 513531, most resulting in profound resistance (32 to256mg/ml). S522L may be the exception, with MICs8 16mg/ml, but these mutants may be unfit andare rarely found in the clinic.4 In E. coli mostmutants in rpoB appear to be uniformly resistantto all rifamycins tested.5 Many M. tuberculosis RIF-resistant mutants are cross-resistant with rifapentine(RIFAP) and rifabutin (RIFAB) but others do showsome differential sensitivity. The M. tuberculosisBeijing strain, well known for its high frequencyof mutations, was equally likely to harbor changesin the rpoB gene as non-Beijing strains.6 Theprevalence of RIF-resistant mutants in a sensitive


152 Rifampin

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology


Guinea pig 4.3±0.7 8.4±1.1 1.2±0.3 Single oral dose of 12 mg/kg16,17

Human 2.46 117.93mg·h/ml 14.91mg/ml Single oral dose of 10 15 mg/kg.15

population is 1×10 6, which is less than the numberof isoniazid (INH)-resistant mutants at 1×10 5.7

In-vitro potency against MTB: M. tuberculosis H37Rv:MIC 0.4mg/ml;8 other authors report MIC values inthe range of 0.1 0.39mg/ml against H37Rv.9,10

Spectrum of activity: RIF is bactericidal with avery broad spectrum of activity against most Gram-positive and some Gram-negative organisms (includ-ing Pseudomonas aeruginosa) and M. tuberculosis[DrugBank].RIF has clinical efficacy against a wide varietyof organisms, including Staphylococcus aureus,Legionella pneumophila, Group-A Streptococcus,Brucella spp., Haemophilus influenzae, and Neisseriameningitidis, as well as in vitro activity against peni-cillin-resistant Str. pneumoniae, N. gonorrhoeae,Chlamydia trachomatis, H. ducreyi, and manyGram-negative rods. Due to rapid emergence ofresistant bacteria it is restricted to treatment ofmycobacterial infections, where the customary useof combination drugs delays resistance development,and the treatment of asymptomatic meningococcalcarriers [DrugBank].Other in-vitro activity: RIF MIC90 for M. tuberculosisis 0.25mg/ml compared with RIFAP 0.06mg/ml.11

RIF exhibited exposure-dependent killing kineticson M. tuberculosis in macrophages, the MIC beingthe same as MIC in broth.12 RIF protein bindingis 83%; this results in an increase in MIC from0.1mg/ml to 1mg/ml in the presence of 50% serum.12

RIF was bactericidal with a 6 log reduction but EC50

(concentration at which half maximum CFU decreasewas observed) decreased over time in culture,demonstrating an exposure (concentration × time)-dependent killing.12 No synergy was observed whenRIF was tested with INH, however significant synergywas seen when RIF and INH were tested in combina-tion with gatifloxacin (GATI) (FIC 0.42), sparfloxacin(FIC 0.39), clarithromycin (CLA), ethambutol (ETH)and streptomycin (STR) (FICs 0.6 0.7).13 Synergyat the MIC level was also seen with RIF incombination with ETH and levofloxacin (LEV), and RIFin combination with ETH, INH and LEV.14

In-vivo efficacy in animal model: The advantagesof RIF as an important sterilizing drug havebeen demonstrated many times in animal models

(reviewed in Mitchison 20007). Various treatmentregimens have been described, perhaps the mostillustrative being complete sterilization of micegiven 25 mg/kg INH and 25 mg/kg RIF for 9 months,but when RIF was withdrawn in the last 3 monthsand INH was continued alone a 20% relapse rate wasobserved (reviewed in Mitchison 20007). Evaluationof the early effects of RIF in mice, with an aerosolinfection model and delayed drug treatment untilinfection reached stationary phase, demonstrateda 3.6 and 4.07 log10 CFU reduction in bacterialburden in the lung using 270 mg/kg with 6 or 12daily doses, respectively. The decrease in CFUs waslinear with dose from 1 to 150 mg/kg/day whenmice were treated for 6 or 12 days. The authorsconcluded that AUC/MIC was the best predictor ofactivity in vivo.12 Increases in dose to 810 mg/kg for6 days did provide sterilization of the mice but thesedose equivalents remain untested in humans due totoxicity concerns.

Efficacy in humansTreatment regime most often used: initially INH,RIF, pyrazinamide (PZA), ETH daily for 2 monthsfollowed by INH and RIF 3 times weekly for4 months [DrugBank]. Specific doses and spe-cific treatment times vary and details can befound in many sources including Centers for Dis-ease Control [http://www.cdc.gov/mmwR/preview/mmwrhtml/rr5211a1.htm] and the World Health Or-ganization [http://www.who.int/en/]. RIF exhibitsvery effective activity against persistors in thecontinuation phase of treatment. Mitchison7 suggeststhat a dose increase from 600 mg to 900 mg dailywould accelerate the sterilization process.

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Mouse: 83% plasma binding.12

• Guinea pig: Bioavailability 51%.• Human: Bioavailability ~70%. At the 600 mg 2×

weekly dose: Cmax: 8 20mg/ml, time to Cmax 1.5 2hour, half-life 2 5 hours, protein binding 85%(reviewed in Burman et al. 200118).

RIF

Rifampin 153

Human metabolic pathway: Metabolism is mainlyhepatic with 13 24% of the drug excreted unchangedin the urine. The drug is present in plasma asparent and deacetyl-RIF. RIF PK/PD is characterizedby auto-upregulation of hepatic and gut metabolismwith time such that the pharmacokinetics of RIFchange with repeated administration; steady stateis usually reached by the sixth daily dose of600 mg/kg. RIF diffuses well to most body tissuesand fluids, including the cerebrospinal fluid (CSF);concentrations in the liver, gallbladder, bile, andurine are higher than those found in the blood;therapeutic concentrations are achieved in thesaliva, reaching 20% of serum concentrations; RIFcrosses the placenta, with fetal serum concentra-tions at birth found to be approximately 33% of thematernal serum concentration; it penetrates intoaqueous humour; it is distributed into breast milk[DrugBank].

Safety and TolerabilityAnimal drug drug interactions: Antagonism occursbetween INH, RIF and PZA in mice (see INH articlefor details).15

Animal toxicity: Acute toxicity: LD50 in mice, rats(mg/kg): 885, 1720 orally; 260, 330 i.v.; 640, 550i.p. [Merck Index].Chronic toxicity: Chronic exposure may cause nauseaand vomiting and unconsciousness [FDA label].Hepatotoxicity: Liver abnormalities were seen inall species tested (rats 5 times, monkeys 8 timesand mice 6 times recommended daily human dose).RIF administered in encapsulated form once ortwice a week was as effective as free drug andshowed less liver toxicity as measured by ALT,alkaline phosphatase and bilirubin levels.19,20 INHand RIF dosed simultaneously in rabbits causedan elevation in phospholipids and a reductionin phosphatidylcholine, cardiolipin and inorganicphosphates, possibly via a choline deficiency, whichmay lead to the observed liver toxicity.21

Reproductive toxicology: Testicular atrophy was seenin baboons at 4 times recommended daily humandose. Teratogenicity was seen in rats at 15 25recommended daily human dose [Physicians’ DeskReference].The available studies on mutagenicity indicateabsence of a mutagenic effect.22 An increaseof hepatomas seen in female mice has beenreported in one strain of mice, following one year’sadministration of RIF at a dosage of 2 10% of themaximum human dosage.22

Animal safety pharmacology: RIF has been reportedto have an immunosuppressive effect in some animalexperiments [FDA label].

Human drug drug interactions: RIF induces certaincytochrome P450s, mainly 3A4 isozyme. The RIF doseof 600 mg/day was established partly to limit theCYP3A induction potential (reviewed in Burman et al.200118).The drug affects the metabolism of the followingdrugs: acetaminophen, astemizole, carbamazepine,corticosteroids, cyclosporin, dapsone, ketoconazole,methadone, phenobarbital, phenytoin, quinidine,terfenadine, theophylline, verapamil and warfarin(reviewed in Douglas and McLeod 199923). Generally,although RIF induces CYP3A and lowers the plasmaconcentrations of some other drugs, its own PKis largely unaffected by this induction. The drugcan also induce CYP1A2, CYP2C and CYP2D6. RIFcauses up to a 70% reduction in the AUC of indinavir,however the CDC has laid out specific guidelines forthe coadministration of the two drugs (reviewed inBurman et al. 200118 and Back et al. 2002;24 seealso Morbidity and Mortality Weekly Reports for CDCguidelines).Human potential toxicity: Hepatotoxicity is gener-ally rare with RIF alone but preexisting conditionscan be exacerbated. A Montreal study showed arate of frank liver toxicity at 0.05/100 followingRIF administration, this was compared with ratesof 3 and 10 times greater for INH and PZA,respectively.25

For RIF (10 mg/kg), clinically apparent hepatotoxic-ity has been reported to occur in 2 5% of cases andaltered liver function tests in 10 15%.26

Human adverse reactions: Hepatitis and serious hy-persensitivity reactions including thrombocytopenia,hemolytic anaemia, renal failure have been re-ported.1 Asymptomatic elevations of serum transam-inase enzymes, increase in serum bile acids andbilirubin concentrations can occur. Marked elevationof serum alkaline, phosphatase and bilirubin suggestsRIF toxicity.Cardiovascular: Hypotension and shock.Respiratory: Shortness of breath.CNS: Rare cases of organic brain syndrome have beenreported (i.e. confusion, lethargy, ataxia, dizzinessand blurring of vision). Peripheral neuropathy,affecting the limbs, muscles and joints in the formof numbness and pain, has been reported.Gastrointestinal: Nausea, vomiting, diarrhoea.RIF causes orange-red staining of all body fluids.

References1. Vernon AA (2003) Rifamycin antibiotics, with a focus

on newer agents. In: Rom WN, Garay SM (editors),Tuberculosis, 2nd edition. Philadelphia, PA: LippincottWilliams & Wilkins, pp. 759 71.

2. Wehrli W, et al. (1968) Interaction of rifamycin withbacterial RNA polymerase. Proc Natl Acad Sci 61, 667 73.

154 Rifampin

3. Engelburg-Kulka H, et al. (2004) Bacterial programmedcell death systems as targets for antibiotics. TrendsMicrobiol 12, 66 70.

4. Huitric E, et al. (2006) Resistance levels and rpoBgene mutations among in vitro-selected rifampin-resistantMycobacterium tuberculosis mutants. Antimicrob AgentsChemother 50, 2860 2.

5. Xu M, et al. (2005) Cross-resistance of Escherichia coli RNApolymerases conferring rifampin resistance to differentantibiotics. J Bacteriol 187, 2783 92.

6. Willams D, et al. (1998) Contribution of rpoB mutationsto development of rifamycin cross-resistance in Mycobac-terium tuberculosis. Antimicrob Agents Chemother 42,1853 7.

7. Mitchison D (2000) Role of individual drugs in thechemotherapy of tuberculosis. Int J Tuberc Lung Dis 4,796 806.


9. Sasaki H, et al. (2006) Synthesis and antituberculosisactivity of a novel series of optically active 6-nitro-2,3-dihydroimidazo[2,1-b]oxazoles. J Med Chem 49,7854 60.

10. Reddy V, et al. (1995) Antimycobacterial activity ofa new rifamycin derivative, 3-(4-cinnamylpiperazinyliminomethyl) rifamycin SV (T9). Antimicrob AgentsChemother 39, 2320 4.


12. Jayaram R, et al. (2003) Pharmacokinetics pharmaco-dynamics of rifampin in an aerosol infection model oftuberculosis. Antimicrob Agents Chemother 47, 2118 24.


14. Rastogi N, et al. (1996) In vitro activities of levofloxacin

used alone and in combination with first- andsecond-line antituberculous drugs against Mycobacteriumtuberculosis. Antimicrob Agents Chemother 40, 1610 6.


16. Pandey R, et al. (2003) Poly (dl-lactide-co-glycolide)nanoparticle-based inhalable sustained drug deliverysystem for experimental tuberculosis. J AntimicrobChemother 52, 981 6.



19. Labana S, et al. (2002) Chemotherapeutic activity againstmurine tuberculosis of once weekly administered drugs(isoniazid and rifampicin) encapsulated in liposomes. IntJ Antimicrob Agents 20, 301 4.

20. Doel P, et al. (1997) Therapeutic efficacies of isoniazid andrifampin encapsulated in lung-specific stealth liposomesagainst Mycobacterium tuberculosis infection induced inmice. Antimicrob Agents Chemother 41, 1211 24.

21. Karthikeyan S (2005) Isoniazid and rifampicin treatmenton phospholipids and their subfractions in liver tissue ofrabbits. Drug Chem Tox 28, 273 80.

22. http://www.inchem.org/23. Douglas J, McLeod M (1999) Pharmacokinetic factors

in the modern drug treatment of tuberculosis. ClinPharmacokinet 37, 127 46.

24. Back D, et al. (2002) Therapeutic drug monitoring inHIV infection: current status and future directions. AIDS16(Suppl), S5 37.

25. Yew W (2002) Clinically significant interactions with drugsused in the treatment of tuberculosis. Drug Saf 25,111 33.

26. Schaberg T, et al. (1995) Risk factors for side-effectsof isoniazid, rifampin and pyrazinamide in patientshospitalized for pulmonary tuberculosis. Eur Respir Rev4, 1247 9.

RIFAP

Tuberculosis (2008) 88(2) 155–158

RifapentineGeneric and additional names: RifapentineCAS name: 3{[(4-cyclopentyl-1-piperazinyl)imino]methyl}-

rifamycinCAS registry #: 61379-65-5Molecular formula: C47H64N4O12Molecular weight: 877.031Intellectual property rights: GenericBrand names: PriftinDerivatives: KRM-1648 (also called Rifalazil or ABI-1648),

rifabutinPolarity: Log P 5.29 [DrugBank]

O

OO

MeOMe

HO

OMe

Me

O

Me

OHOH

Me

Me

NH

OMeOH

OH

Me

NN

N

Formulation and optimal human dosage: 600 mg 2× weeklyCapsules 150 mg Aventis

Basic biology informationDrug target/mechanism: See rifampin (RIF).Drug resistance mechanism: As with RIF, most ofthe clinical Mycobacterium tuberculosis mutationsresulting in resistance to rifapentine (RIFAP) andKRM-1648 (RIFAL) are in the rpoB gene, generallyconfined to the rif-resistance determining region(RDR). Some mutations confer resistance to all therifamycin analogs whereas others were found to bespecific to RIF and RIFAP but not to RIFAL or rifabutin(RIFAB).1 A significant number of publications onthese mutations can be found1 3 and most of theauthors agree that both position and type of sub-stitution play a role in sensitivity to the rifamycins:as a general rule, mutations at codons 511 and 516result in resistance to RIF and RIFAP but sensitivityto RIFAL and RIFAB, while mutations at codon 531result in high-level resistance to all the rifamycinanalogs. A few rifamycin-resistant mutations arefound outside the RDR; in Escherichia coli there aresome mutational hot spots outside the core regionof rpoB which result in rifamycin resistance, and thesame may apply in M. tuberculosis. No RIF-resistantM. tuberculosis mutations outside rpoB have beenmapped, but mutations outside the RDR or alterationin drug transporters or membrane permeability aresuspected in these cases.2

In-vitro potency against MTB: M. tuberculosis H37RvMICs: RIFAP 0.031mg/ml, RIFAB <0.015mg/ml, RIF0.25mg/ml.1

Spectrum of activity: RIFAB and RIFAP are activeagainst the same spectrum of mycobacteria as RIFalthough differences in absolute MICs have beenidentified. RIFAB and RIFAP are more active thanRIF in vitro against the M. avium complex (MAC),M. tuberculosis, and M. leprae.4,5

Other in-vitro activity: RIFAP MIC: M. africanumATCC 25420 0.031mg/ml, M. bovis ATCC 192100.063mg/ml.RIFAP metabolite 25-O-deacetyl-RIFAP MIC: M. afri-canum ATCC 25420 0.125mg/ml, M. bovis ATCC 192100.125mg/ml. MICs for other strains are provided inthe same paper.6

Yang2 ranks the rifamycins in the following order ofdecreasing MIC: RIF > RIFAP > RIFAL.Activity against M. avium: MIC RIFAB 0.06mg/ml;RIFAP 0.0125mg/ml.7

Post-antibiotic effects were measured with RIFAPgiving 20 hours at 20mg/ml, the longest comparedwith isoniazid (INH) and moxifloxacin (MOXI); theaddition of MOXI (2mg/ml) to RIFAP (10mg/ml)increased this to 137 hours.8

RIFAP was more efficacious than RIFAB againstToxoplasma gondii in vitro, but atovaquone, a knownT. gondii treatment, outperformed them both. Nohost-cell toxicity was observed at efficacious levelsof 10mg/ml. RIFAP and RIFAB were active in vivo in amouse model, where they showed superior activityto atovaquone at 50 mg/kg but inferior activity at


156 Rifapentine

100 mg/kg. Again RIFAP outperformed RIFAB at bothlevels.9

In-vivo efficacy in animal model: Mouse studiesin a M. tuberculosis model demonstrated thathigh RIFAP (equivalent to 10 15 mg/kg in humans)was more effective than a lower dose (equivalentto 5 mg/kg in humans).10 Treatment failure wasobserved with all weekly dose regimens using RIFAPalone, but successful outcomes resulted when RIFwas substituted for RIFAP in the continuation phase;specifically, INH, RIF and pyrazinamide (PZA) weregiven for two months daily followed by RIFAP,INH weekly for four months.10 The antimicrobialactivities of RIF, RIFAB and RIFAP were comparedin BCG-vaccinated and M. tuberculosis-infectedimmunocompetent mice. Using an equal weight basisboth RIFAP and RIFAB were more bactericidal thanRIF. The activity of RIF was significantly reducedwhen drug was administered to mice three timesa week instead of six times a week, howeversignificant bactericidal activity was still observed inmice treated with RIFAP, 10 mg/kg up to once everytwo weeks, or RIFAB, 10 mg/kg twice weekly. Thebactericidal activity of RIFAB, 10 mg/kg 6×/week for6 weeks, or RIFAP, 10 mg/kg 2×/week for 12 weeks,was comparable to that of RIF, 10 mg/kg 6×/weekfor 12 weeks in mice.11 Pharmacokinetic experimentscomparing RIF, RIFAB and RIFAP demonstrated thatRIFAP had the highest serum peak level (Cmax) andthe longest half-life, whereas RIFAB displayed thelowest Cmax and the shortest half-life.11 Chapuiset al.12 showed various degrees of bactericidalactivity in mice after daily treatment with RIF plusPZA for 13 weeks, INH daily for 26 weeks, or RIFAPonce weekly for 13 or 26 weeks or once everytwo weeks for 26 weeks. The activity of RIFAPwas significantly enhanced when INH was addedat the same dosing frequency. After chemotherapywas stopped no relapses or very few relapses wereobserved in normal mice that had been treatedwith RIF + PZA daily for 13 weeks, or RIFAP aloneor RIFAP+ INH once weekly for 26 weeks. Thelatter three regimens and RIFAP+ INH once weeklyfor 13 weeks may be applied for fixed-durationpreventive therapy in human immunodeficiency virus(HIV)-negative subjects.12 Previously it had beenshown in mice that the most active weekly regimen(RIF, MOXI, INH) was less effective than the standard6-month daily regimen recommended by the WHO(RIF, INH, PZA).13 Using a similar mouse model withweekly treatments, RIFAP increased to 15 mg/kg andMOXI increased to 400 mg/kg, there was relapse in11% of cases 3 months after treatment cessation.Regardless of RIFAP dose relapse was completelyablated if mice were treated with a regimen which

included MOXI at 400 mg/kg for 5/7 days for the first2 weeks.14

In vivo (mouse) against M. avium RIFAB showedbetter activity than RIF and slightly better activitythan RIFAP.7

Efficacy in humansRIFAP was approved for human use in 1998. Itis a long-acting rifamycin with use restricted toHIV-negative patients who are sputum negative attwo months post treatment (reported in Veziriset al. 200514). The clinical data generated withthis drug strive to quantitate the effect of RIFAP’s12-hour half-life, high plasma binding (~98%) withthe obvious benefits of weekly dosing. A 2004study15 reported that there were no drug-relatedadverse effects from once weekly RIFAP at up to1200 mg. The study was conducted to evaluate thehigh dose and concluded that further trials werejustified.15 Similarly, Weiner et al.16 demonstratedthat low INH serum concentrations were associatedwith the failure of the weekly RIFAP/INH regimen.Weekly RIFAP success was documented for thetreatment of latent TB in high-risk situations17

when it was shown that weekly RIFAP/INH (900 mgof each for 12 weeks) was better tolerated thandaily RIF/PZA (RIF 450 600 mg/PZA 750 1500 mg for8 weeks); efficacy was almost the same in the twogroups, with 0.52% relapse in the daily treatmentgroups and 1.46% failure in the weekly treatment.The sterilizing effects of RIFAP versus RIF werecompared in an EBA study;18 five daily doses of RIF(150 600 mg) or one dose of RIFAP (300 1200 mg)were compared and data showed that the 1200 mgdose of RIFAP was necessary to prevent bacterialregrowth and development of RIF resistance. Burmanet al.19 note that both RIFAB and RIFAP exhibitidiosyncratic clinical efficacy; RIFAB is active despiteunfavorable Cmax/MIC ratios while RIFAP exhibitssub-optimal clinical performance despite a veryfavorable Cmax/MIC ratio; these phenomena may bepartly explained by differences in protein bindingand in intracellular penetration (reviewed in Burmanet al. 200119).

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Mouse: Half-life of the compound alone is 14 18

hours.21

• Human: RIFAP was 70% bioavailable [FDA label].RIFAP is 97% protein bound; ratio of extracellularto intracellular concentration is 24 60 for RIFAP,and 5 for RIF.19 Repeated doses do not appear toaffect clearance of RIFAP but do affect clearanceof RIF and RIFAB; with repeated doses the AUC of

RIFAP

Rifapentine 157

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Mouse 309±35.5*,474±5.8**

11.1±0.39*,16.7±1.1*

Single dose in mice of *10 mg/kgand **15 mg/kg with single dose ofMOXI 100 mg/kg20

Human 13.19±7.38 319.54±91.52 15.05±4.62 2.03±0.6 l/h Dose 300 mg/day, PK determined atday 10 [FDA label]. PK for the25-deactyl RIFAP metabolite is asfollows: T1/2 = 13.35±2.67 h;Cmax = 6.26±2.06mg/ml;AUC = 215.88±86mg·h/ml[FDA label].

RIFAB is lowered but the half-life is unaffected.Steady-state levels of RIF and RIFAB are achievedafter 6 days of daily dosing (reviewed in Burmanet al. 200119).

Animal metabolic pathway: In rat, RIFAP was rapidlytaken up by the liver but diffused slowly into tissues.Oral absorption was 84% after a 3 mg/kg dose. Higherconcentration was found in lungs compared withplasma. 92% of the dose is eliminated in faeces.21

Human metabolic pathway: About 10% of RIFAP isexcreted unchanged in the urine compared with13 24% of RIF. Plasma elimination half-life is 14 18hours.19 17% and 70% of the total dose was recoveredin urine and faeces, respectively, and >80% ofthe total dose was excreted within 7 days. RIFAPand 25-O-deacetyl-RIFAP accounted for 99% of thetotal radioactivity in plasma. Slight gender-relateddifferences in PK were observed [FDA label].

Safety and TolerabilityAnimal toxicity: Teratogenic effects: RIFAP wasteratogenic in rats and rabbits. In rats at 0.6× thehuman dose equivalents given during organogenesissome pups had cleft palate, delayed ossificationand an increase in the number of ribs. In rabbitsat 0.3 1.3× human dose equivalents 4 of 431pups had irregular ossification of facial tissues,arhinia and microphthalmia and abnormalities inovarianagenesis.Non-teratogenic effects: Increases in stillborn pupswere found in rats and rabbits at 0.3× and 1.3×human dose equivalents, respectively [DrugBank].Carcinogenicity: RIFAP was negative in the Ames test,the in vitro point mutation test in A. nidulans,gene conversion assay in Saccharomyces cerevisiae,CHO/HGRPT forward mutation assay, and others.25-deacetyl-RIFAP was positive in an in vitrochromosomal aberration assay [FDA label].Human drug drug interactions: In general therifamycins do induce CYP3A in gut and liver butnot in neutrophils and lymphocytes. The relative

induction of CYP3A by the rifamycins is RIF >RIFAP > RIFAB, although this is generally reversed 1 2weeks following drug cessation (reviewed in Burmanet al. 200119). Other microsomal enzymes arealso affected, namely CYP1A2, CYP2C and CYP2D6.Rifamycins in general should not be given with azoleantifungals as subtherapeutic serum concentrationsof the latter can result (reviewed in Burmanet al. 200119) although the FDA label indicates adecrease in the drug levels of itraconazole, but notfluconazole, when given with RIFAB.Human potential toxicity: The “flu-like” symptomsobserved with RIF treatment are not seen asfrequently with RIFAP19 when 2× weekly RIF and1× weekly RIFAP are compared. This may be dueto a decreased immune reaction to RIFAP comparedwith RIF, or because RIFAP has a longer half-life thusexposing the immune system to a distinct regimen ofdrug.19

Human adverse reactions: Hepatitis frequency issimilar to that seen with RIF, and probably notassociated with the rifamycins but with drugcombinations.19

Cardiovascular: similar to RIF.Respiratory: similar to RIF.CNS: similar to RIF.Gastrointestinal: similar events and frequency aswith RIF, RIFAB and RIFAP (nausea, vomiting,diarrhoea).Similar as with RIF, skin and body-fluid discolorationmay result from RIFAP dosing [FDA label].

References1. Williams D, et al. (1998) Contribution of rpoB mutations

to development of rifamycin cross-resistance in Mycobac-terium tuberculosis. Antimicrob Agents Chemother 42,1853 7.


158 Rifapentine

3. Saribas Z, et al. (2003) Rapid detection of rifampinresistance in Mycobacterium tuberculosis isolates byheteroduplex analysis and determination of rifamycincross-resistance in rifampin-resistant isolates. J ClinMicrobiol 41, 816 8.

4. Kunin C, et al. (1996) Antimicrobial activity of rifabutin.Clin Infect Dis 22(Suppl 1), S3 13. Discussion: S13 4.


6. Rastogi N, et al. (2000) Activity of rifapentineand its metabolite 25-O-desacetylrifapentine comparedwith rifampicin and rifabutin against Mycobacteriumtuberculosis, Mycobacterium africanum, Mycobacteriumbovis and M. bovis BCG. J Antimicrob Chemother 46,565 70.

7. Klemens S, et al. (1991) In vivo activities of newerrifamycin analogs against M. avium infection. AntimicrobAgents Chemother 35, 2026 30.

8. Chan C, et al. (2004) In vitro postantibiotic effects ofrifapentine, isoniazid, and moxifloxacin against Mycobac-terium tuberculosis. Antimicrob Agents Chemother 48,340 3.

9. Araujo F, et al. (1996) Rifapentine is active in vitroand in vivo against Toxoplasma gondii. Antimicrob AgentsChemother 40, 1335 7.

10. Daniel N, et al. (2000) Antituberculosis activity ofonce-weekly rifapentine-containing regimens in mice.Long-term effectiveness with 6- and 8-month treatmentregimens. Am J Respir Crit Care Med 161, 1572 7.

11. Ji B, et al. (1993), Effectiveness of rifampin, rifabutin,and rifapentine for preventive therapy of tuberculosis inmice. Am Rev Respir Dis 148, 1541 6.

12. Chapuis L, et al. (1994) Preventive therapy of tuberculosis

with rifapentine in immunocompetent and nude mice. AmJ Respir Crit Care Med 150, 1355 62.

13. Lounis N, et al. (2001) Effectiveness of once-weekly rifapentine and moxifloxacin regimens againstMycobacterium tuberculosis in mice. Antimicrob AgentsChemother 45, 3482 6.

14. Veziris N, et al. (2005) Efficient intermittent rifapentinemoxifloxacin-containing short-course regimen for treat-ment of tuberculosis in mice. Antimicrob AgentsChemother 49, 4015 9.

15. Weiner M, et al. (2004) Pharmacokinetics of rifapentine at600, 900, and 1,200 mg during once-weekly tuberculosistherapy. Am J Respir Crit Care Med 169, 1191 7.

16. Weiner M, et al. (2003) Low isoniazid concentrationsand outcome of tuberculosis treatment with once-weeklyisoniazid and rifapentine. Am J Respir Crit Care Med 167,1341 7.

17. Schechter M, et al. (2006) Weekly rifapentine/isoniazidor daily rifampin/pyrazinamide for latent tuberculosisin household contacts. Am J Respir Crit Care Med 173,922 6.

18. Sirgel F, et al. (2005) The early bactericidal activities ofrifampin and rifapentine in pulmonary tuberculosis. Am JRespir Crit Care Med 172, 128 35.


20. Rosenthal I, et al. (2005) Weekly moxifloxacin andrifapentine is more active than the Denver Regimen inmurine tuberculosis. Am J Respir Crit Care Med 172,1457 62.

21. Assandri A, et al. (1984) Pharmacokinetics of rifapentine,a new long lasting rifamycin, in the rat, the mouse andthe rabbit. J Antibiot Tokyo 37, 1066 75.

SQ109

Tuberculosis (2008) 88(2) 159–161

SQ109Generic and additional names: SQ-109

NSC722041SQ109 Ditrifluoroacetate salt, HCl salt

CAS name: N-[(2E)-3,7-dimethyl-2,6-octadienyl]-N′-tricyclo[3.3.1.13,7]dec-2-yl-1,2-ethanediaminedihydrochloride

CAS registry #: 627526-76-5Molecular formula: C22H38N2Molecular weight: 330.6Intellectual property rights: Sequella

HN

NH

Me

Me

Me

Derivatives: A combinatorial library of 67,238 analogs was made based on the ethylene-diamine core ofethambutol1,2

Polarity: Calculated log P (KowWin): 6.45 [NAID home AIDS # 207396]

Basic biology informationDrug target/mechanism: SQ109 is a novel 1,2-ethyl-enediamine-based ethambutol (ETH) analog; nospecific studies on mode of action are available. Noeffects on EmbA or -B, the target of ETH, were seenwith a proteomic approach comparing the effects of24-hour drug on Mycobacterium tuberculosis H37Rv.A few proteins, such as ATP-dependent DNA/RNA he-licase and b-keto-acyl-acyl carrier protein synthase,were differentially regulated by isoniazid (INH) andSQ109 or ETH; INH treatment resulted in down-regulation of the helicase and up-regulation of thesynthase whereas treatment with ETH or SQ109resulted in up-regulation of the helicase and down-regulation of the synthase.3

Based on activity against ETH-resistant strains anddifferences in behavior of ETH and SQ109 in gene-array studies Protopopova et al.1,4 postulate thatSQ109 has a distinct mechanism of action oractivating mechanism compared with ETH.Drug resistance mechanism: Specific resistancemechanisms were not studied but SQ109 was activeagainst RIF-resistant organisms.4

In-vitro potency against MTB: M. tuberculosisH37Rv MICs reported by Sequella: MIC 0.11mg/ml(BACTEC), MIC 0.35mg/ml broth dilution.2 MICson drug-sensitive and -resistant clinical isolates0.16 0.64mg/ml, indistinguishable from H37Rv.4

Sequella also reported SQ109 MICs in a separatepublication: M. tuberculosis Erdman 0.7mM; M. tu-

berculosis ETH-resistant 1.4mM in Alamar Blue,0.99mM in BACTEC; M. tuberculosis INH-resistant1.4mM; M. tuberculosis RIF-resistant �0.7.1

Spectrum of activity: SQ-109 is somewhat specificfor mycobacteria: M. tuberculosis 0.25 5mg/ml,M. bovis 0.25mg/ml, and M. marinum 8mg/ml,5

but little activity against M. avium and M. smeg-matis.4 Some activity against Candida albicans(4 8mg/ml) including fluconazole-resistant strains,5

other analogs of this class being tested.Other in-vitro activity: Synergistic activity wasobserved between SQ109 and INH or rifampin(RIF) against H37Rv. Synergy between SQ109, butnot ETH, and RIF was found using RIF-resistantstrains. Additive effects occurred with streptomycin(STR) and SQ109; no synergistic effects, positiveor negative, were seen between pyrazinamide(PZA) or ETH and SQ109.4 Intracellular activityagainst M. tuberculosis-infected RAW cells: MIC99

0.5mg/ml.1

In-vivo efficacy in animal model: SQ109 was effectiveas an oral dose in mice (drug administered 20 daysafter infection, drug 5× weekly for 45 days at1 mg/kg) and is 100 times more effective thanETH; highest activity observed in lung.1 Oraladministration of SQ109 (0.1 25 mg/kg) was dosedependent and 10 25 mg/kg was as effective asETH at 100 mg/kg but less effective than INH at25 mg/kg.6 Low protein binding was observed withSQ109.7


160 SQ109

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Mouse 5.2±1.1* 0.254±0.184* 0.135±0.01* 11.83±1.49** 3788±1768ml/kg/h**

*Oral dose of 25 mg/kg,**i.v. dose of 3 mg/kg.6

Rat 8.2* 0.99* 0.64* 9.96** 1575 ml/kg/h** *13 mg/kg single oral,**1.5 mg/kg i.v.dose7

Dog 19.6±4.8* 0.087±0.016* 0.011±0.002* 29.2±6.9** 2471±319ml/kg/h**

*3.75 mg/kg single oral,**4.5 mg/kg i.v. dose7

Substitution of EMB (100 mg/kg) with SQ109 (10 mg/kg) in a regimen containing RIF and INH resultedin better clearance of tissue bacteria and 25 30%decrease in time to standard of care effects,whether or not PZA was included in the regimen, orwhether analysis was done at 1 or 2 months.8

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Mouse: Oral bioavailability 8%.7,9 Levels in lung

and spleen were up to 120-fold higher than inplasma, and 10× higher than MIC.6

• Rat: Oral bioavailability 12%, highest drug concen-tration in liver > lung > spleen > kidney.7

• Dog: SQ109 partially degrades (30 40%) in dogand human plasma but is stable in rat andmouse plasma.9 Very high clearance and volumeof distribution was found in dog compared withmouse and rat, oral bioavailability 2.4 5%.7

• Human: SQ109 degraded in dog and human plasmabut was stable in rat and mouse plasma.9 Plasmabinding is higher (10 20%) in humans comparedwith 5 10% in rat and mouse.7

Animal metabolic pathway: Elimination of drug inthe urine (22%) and in faeces (5.6%) was observed inrats dosed with labeled compound.7

Human metabolic pathway: In vitro analysisof microsomal treatment showed the compoundis metabolized by oxidation, epoxidation andN-dealkylation.7

Safety and TolerabilityAnimal drug drug interactions: The compound ismetabolized in the presence of liver microsomesto the following extent in a 10-minute incubation:mouse 48%, rat 23%, dog 51%.7

Animal toxicity: Metabolism seems to be extensiveboth in the animal and in vitro, and the toxicityprofile for these molecules needs to be examined.7

Human drug drug interactions: The compound ismetabolized by CYP2D6 and CYP2C19, up to 58% ofparent being metabolized in 10-minute incubation

with microsomes; insignificant metabolism is foundin the presence of CYP3A4.7

Human potential toxicity: A phase-1 double-blind,placebo-controlled study completed in May 2007found that oral doses of SQ109 up to 300 mg, thehighest dose tested, were safe and well tolerated,with no serious adverse effects reported at any dose.No measurable clinically meaningful changes in bloodchemistry, haematology or ECG were observed, thedrug had a wide tissue distribution, and plasma levelswere as expected from animal studies. The drugdoes have a long half-life of 61 hours [Sequella pressrelease, May 2007].“Sequella plans to conduct an additional Phase 1bclinical study to demonstrate safety of daily admin-istration of SQ109 alone, and then in combinationwith other TB drugs to evaluate safety and efficacyin patients with pulmonary TB. Additional clinicalstudies will begin Q2 2007.” [Sequella press release,May 2007].

References1. Protopopova M, et al. (2005) Identification of a new anti-

tubercular drug candidate, SQ109, from a combinatoriallibrary of 1,2-ethylenediamines. J Antimicrob Chemother56, 968 74.

2. Lee R, et al. (2003) Combinatorial lead optimization of[1,2]-diamines based on ETH as potential anti-tuberculosispreclinical candidates. J Comb Chem 5, 172 87.

3. Jia L, et al. (2005) Pharmacoproteomic effects of isoni-azid, ethambutol, and N-geranyl-N-(2-adamantyl)ethane-1,2-diamine (SQ109) on Mycobacterium tuberculosisH37Rv. J Pharmacol Exp Ther 315, 905 11.

4. Chen P, et al. (2006) Synergistic interactions of SQ109,a new ethylene diamine, with front-line antituberculardrugs in vitro. J Antimicrob Chemother 58, 332 7.

5. Barbosa, et al. (2006) In vitro antifungal susceptibilitytesting of drug candidate SQ109 against Candida albicans.Presented at Interscience Conference on AntimicrobialAgents and Chemotherapy (ICAAC), San Francisco, CA.Poster F1 1371.

6. Jia L, et al. (2005) Pharmacodynamics and pharmacokinet-ics of SQ109, a new diamine-based antitubercular drug.Br J Pharmacol 144, 80 7.

7. Jia L, et al. (2006) Interspecies pharmacokinetics andin vitro metabolism of SQ109. Br J Pharmacol 147,476 85.

SQ109

SQ109 161

8. Nikonenko BV, et al. (2007) Drug therapy of experimen-tal TB: improved outcome by combining SQ109, newdiamine antibiotic, with existing TB drugs. AntimicrobAgents Chemother 51, 1563 5.

9. Jia L, et al. (2005a) Simultaneous estimation ofPK properties in mice of 3 anti-tubercular ethambutolanalogs obtained from combinatorial lead optimization.J Pharmaceut Biomed Anal 37, 793 9.

Tuberculosis (2008) 88(2) 162–163

StreptomycinGeneric and additional names: Streptomycin ACAS name: O-2-Deoxy-2-(methylamino)-a-l-glucopyranosyl-(12)-O-5-deoxy-3-C-

formyl-a-l-lyxofuranosyl-(14)-N,N′-bis(aminoiminomethyl)-d-streptamineCAS registry #: 57-92-1Molecular formula: C21H39N7O12Molecular weight: 581.57Intellectual property rights: GenericBrand names: Sesquisulfate-AgriStrep (Merck & Co.); Streptobrettin (Norbrook);

Vetstrep (Merck & Co.).Solubility: The salts are very soluble in water; but almost insoluble in alcohol,

chloroform, ether [Merck Index].Polarity: Log P 8.005 [DrugBank]

NH

OHO

HO

O

Me

OHC

O

OHOHO

HO

HN Me

OH

NHH2N

HN

H2N NH

Formulation and optimal human dosage: Dose 1 g daily i.v. or intramuscularly (i.m.)1

Basic biology informationDrug target/mechanism: Streptomycin (STR) was thefirst aminoglycoside antibiotic identified; it inhibitsprotein synthesis by binding tightly to the conservedA site of 16S rRNA in the 30S ribosomal subunit(reviewed in Chan et al. 20031). It is in the sameclass as amikacin (AMI) and kanamycin (KAN).Drug resistance mechanism: Ribosomal changesin the 16S rRNA and ribosomal protein S12 areassociated with STR resistance in Mycobacteriumtuberculosis.1,2 Cross-resistance with other classmembers (KAN and AMI) and the macrocyclepolypeptide capreomycin (CAP) exists, but this isnot always complete or reciprocal; for example,3

KAN, AMI and CAP were still efficacious in vitro whenresistance to STR had developed.3 In general AMIappears to be active against STR-resistant strains ofM. tuberculosis while strains resistant to AMI areequally resistant to STR. CAP is generally activeagainst STR-resistant M. tuberculosis strains butCAP-resistant strains are often sensitive to AMI.2

In-vitro potency against MTB: M. tuberculosis H37Rv:MIC 1mg/ml.4

Spectrum of activity: Aminoglycosides are usedmainly in infections involving aerobic, Gram-negative bacteria, such as Pseudomonas, Acineto-bacter and Enterobacter. M. tuberculosis is alsosensitive to this drug. Gram-positive bacteria canalso be treated with the drug but less toxicalternatives tend to be utilized. Synergistic effects

with the aminoglycosides and beta lactams haveresulted in use of this combination treatmentfor streptococcal infections, especially endocarditis[DrugBank].Other in-vitro activity: STR is active (MIC 1mg/ml)against H37Rv and a number of M. tuberculosisclinical strains including an MDR strain withresistance to isoniazid (INH) and rifampin (RIF).4

In a study comparing the bactericidal activityof several agents, RIF and INH were superioragainst drug-sensitive strains followed by ethion-amide (ETA) and STR, with ethambutol (ETH)and cycloserine (CYS) having marginal bactericidalactivity.4

STR had no bactericidal activity, but did causesignificant reduction in bacterial load when M. tu-berculosis-infected macrophages were treated usingaminoglycosides; there was a 1 2 log reduction inCFU, 99% killing using STR 30mg/ml or KAN 30mg/mlor AMI 20mg/ml.4

In-vivo efficacy in animal model: AMI was the mostactive of the aminoglycosides tested (STR, AMI andKAN dosed at 200 mg/kg 6 times weekly) in a mousemodel of tuberculosis (2.3×107 CFU M. tuberculosisadministered i.v. followed by dosing 1 day later).STR reduced the CFU in the spleen by almost1 log. All three drugs were less efficacious thanINH at 25 mg/kg. All the mice in the drug-treatedgroups survived whereas the control mice died within30 days.5


STR

Streptomycin 163

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Human 25 50 1 g i.m. Following intramuscular in-jection of 1 g of STR, as the sulfate,a peak serum level of 25 50mg/mlis reached within 1 hour,diminishing slowly to about 50%after 5 6 hours [DrugBank].

Efficacy in humansSTR was the first drug approved for the treatmentof tuberculosis following human trials in 1947.STR is the least toxic of the three aminoglycosides,STR, AMI and KAN.6 It is clinically effective asa single agent but resistance development isunacceptably rapid. The aminoglycosides cannotbe administered orally. Historically prescribed withINH, STR probably had little overall effect in thiscombination (reviewed in Grosset and Ji 19987).Aminoglycosides remain important drugs for treatingdiseases caused by M. tuberculosis (reviewed inPeloquin et al. 20046) but they are no longerfirst line.

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Human: All the aminoglycosides are administered

parenterally. Chan et al.1 give a value for Cmax of35 45mg/ml, with no dose given.

Human metabolic pathway: Primarily eliminatedthrough the kidney, between 29% and 89% of a600 mg dose is excreted in the urine within 24 hours[DrugBank]. STR passes through the placenta withserum levels in the cord blood similar to maternallevels. Small amounts are excreted in milk, saliva,and sweat.

Safety and TolerabilityAnimal toxicity: Oral rat with STR sulfate LD50430 mg/kg; side effects include nausea, vomiting,and vertigo, paraesthesia of face, rash, fever,urticaria, angioneurotic edema, and eosinophilia[DrugBank].Human drug drug interactions: Concurrent use ofother aminoglycosides and gentamycin, tobramycin,viomycin and cyclosporin is not recommended. Careshould be taken post anaesthesia or post dosing withmuscle relaxants as respiratory paralysis can occur[DrugBank].Human potential toxicity: STR for use in humanscarries a warning about serious neurotoxic effects;

risk of severe neurotoxic reactions (includingcochlear and vestibular dysfunction, optic nervedysfunction, peripheral neuritis, arachnoiditis, andencephalopathy) increases in patients with impairedrenal function or pre-renal azotemia [FDA label].8th Cranial Nerve, ototoxicity and nephrotoxicity.2

The aminoglycosides and CAP are known for theirototoxicities, and incidences may be as highas 3 10%.1 The following reactions are common:vestibular ototoxicity (nausea, vomiting, and ver-tigo); paraesthesia of face; rash; fever; urticaria;angioneurotic edema; and eosinophilia [DrugBank].Human adverse reactions: STR is contraindicated inpatients with renal impairment. The toxicity seenin renal impaired patients is directly linked to theinability to excrete the drug at the same rate asnormal individuals [DrugBank].

References1. Chan E, et al. (2003) Pyrazinamide, ethambutol,

ethionamide, and aminoglycosides. In: Rom WN, Garay SM(editors), Tuberculosis, 2nd edition. Philadelphia, PA:Lippincott Williams & Wilkins, pp. 773 789.


3. Ho Y, et al. (1997) In-vitro activities of aminoglycoside-aminocyclitols against mycobacteria. J AntimicrobChemother 40, 27 32.

4. Rastogi N, et al. (1996) In vitro activities of fourteenantimicrobial agents against drug susceptible and resistantclinical isolates of Mycobacterium tuberculosis andcomparative intracellular activities against the virulentH37Rv strain in human macrophages. Curr. Microbiol, 33,167 175.




Tuberculosis (2008) 88(2) 164–167

ThioridazineGeneric and additional names: Thioridazine;

2-methylmercapto-10-[2-(N-methyl-2-piperidyl)ethyl]phenothiazine;3-methylmercapto-N-[2′-(N′-methyl-2-piperidyl)ethyl]phenothiazine;Thioridazine-2-sulfoxide

CAS name: 10-[2-(1-Methyl-2-piperidinyl)ethyl]-2-(methylthio)-10H-phenothiazineCAS registry #: 50-52-2Molecular formula: C21H26N2S2Molecular weight: 370.57Intellectual property rights: Generic

N

S

N

H

MeS

Me

Brand names: Aldazine (Alphapharm); Mellaril, Melleretten, Mallorol (Novartis); Novoridazine (Novopharm);Orsanil (Orion); Ridazin (Taro); Stalleril (Pharmacal)

Solubility: Soluble in alcohol (1 in 6), chloroform (1 in 0.81), ether (1 in 3); freely soluble in dehydratedalcohol; practically insoluble in water at 0.0336 mg/l [Merck Index].

Polarity: Log P 6.552 [DrugBank]Acidity/basicity: pKa 9.5 [DrugBank].Melting point: 73ºC [DrugBank]Formulation and optimal human dosage: The usual starting dose for adult schizophrenic patients is 50 100 mg

three times a day, with a gradual increment to a maximum of 800 mg daily if necessary. Supplied as oralsuspension or as tablets from 10 to 200 mg. Some phenothiazines can be administered i.v.

Basic biology informationDrug target/mechanism: Thioridazine (THZ) is aphenothiazine; other members of this class in-clude chlorpromazine and trifluoperazine. Theseclosely related compounds and their analogsare active against TB and have been used toprobe the mechanism of action of the pheno-thiazines as TB agents. Phenothiazines in gen-eral, and THZ in particular, have been describedas exerting their anti-tuberculosis effects viacalmodulin1,2 or by inhibiting NADH2-menaquinone-oxidoreductase (Ndh2).3 The phenothiazines, es-pecially THZ, are also inhibitors of the voltage-gated Kv 1.3 channels and are thought to exerttheir anti-psychotic activity through a blockade ofdopamine receptors, particularly the D2 popula-tions.4

Calmodulin: the evidence for calmodulin involve-ment is circumstantial; calmodulin-type genes havebeen found in Mycobacterium tuberculosis,1 thephenothiazines have been described as calmodulinantagonists,4 and trifluoperazine, a related pheno-thiazine, has been crystallized with calmodulin invarious stoichiometries.5

Ndh2: Several authors6,7 have demonstrated that thephenothiazines inhibit succinate dehydrogenase andtype II NDH (NADH-quinone oxidoreductase),7 causedepletion of ATP levels, and alter NADH/NAD andmenaquinol/menaquinone ratios;6 these activitiesimplicate oxidative phosphorylation as the targetfor phenothiazines.6,7 Trifluoperazine and two closelyrelated analogs inhibit Ndh2 with an IC50 around12mM.3 Trifluoperazine inhibits the consumption ofoxygen in isolated M. tuberculosis membranes at asite upstream of cytochrome C.7 Ndh2, part of theelectron transport chain and therefore implicatedin oxygen consumption, is a non-proton-pumpingoxidoreductase present in two forms, Ndh and NdhA,and chlorpromazine inhibits both subtypes with anIC50 of 10mM.7

In-vitro potency against MTB: M. tuberculosis ATCC27294: MIC 10mg/ml compared with chlorpromazine15mg/ml.8

Spectrum of activity: The phenothiazines as aclass have shown antibacterial activity against themycobacteria.8 Chlorpromazine has shown activityagainst Staphylococcus aureus, Enterococcus fae-calis, Escherichia coli, M. tuberculosis, atypical


THZ

Thioridazine 165

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Human 30±7 25 150ng/ml

21±9 8.6±2.9ml·min/kg

Chlorpromazine probably 100 mgoral dose [Goodman & Gilman’s,pp. 497 8].

mycobacteria, influenza virus, measles virus, andherpes simplex virus. Phenothiazines as a classhave shown activity against intestinal anaerobes,Bacteroides spp., Prevotella spp. and Fusobacterium(reviewed in Kristiansen and Amaral 19979). THZ hasdemonstrable activity against Trypanosoma cruziin vitro and in vivo.10,11 THZ had activity against twostrains of malaria, the 3D7 drug-resistant strain andthe W2 drug-sensitive strain, with IC50s of 2.6 and1.9mM, respectively; this activity is thought to betarget-based as a number of THZ analogs includingchlorprothixene were also active.12

Other in-vitro activity: Phenothiazines appear tobe equally active on starved (representative ofpersistent state) or log phase cells unlike rifampin(RIF), which has some activity on the starvedcells, or isoniazid (INH), which has no activity onstarved cells.13 Synergistic activity at the MIC levelbetween RIF and streptomycin (STR), but notINH, and the phenothiazines has been reported.14

MICs for phenothiazines are much higher than thecorresponding values in macrophages as the drugconcentrates inside cells.8 The MICs in macrophagesfor inhibiting M. tuberculosis growth have beenreported as 0.23 3.6mg/ml15 and 0.1mg/ml.8 In thelatter studies there were no cytotoxic effects onthe macrophages at the concentrations required forefficacy.8 Finally, Bate et al.16 demonstrated thatnovel phenothiazine derivatives inhibited M. tuber-culosis in the non-replicating state at MICs thatwere lower than those under actively growingconditions.In-vivo efficacy in animal model: Weak in vivoefficacy (1 log reduction from control compared with3 logs for RIF at 12.5 mg/kg) was achieved witha phenothiazine analog at 100 mg/kg for 11 daysin an acute model where drug was administeredon infection and one day post infection.7

Efficacy in humansNo published data are available, but there aresuggestions that THZ is being used in the clinicpresumably for MDR and XDR cases. One group haverecommended treatment with THZ for compassion-ate use in TB patients.17

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Human: Chlorpromazine has 32% oral bioavail-

ability but may decrease to ~20% with repeateddose, 95% protein bound [Goodman & Gilman’s,pp. 497 8].

Animal metabolic pathway: In rats sulfoxidationin position 2 of the thiomethyl substituent andin the thiazine ring are main metabolic pathwaysof THZ. In contrast to humans, in the ratN-desmethylthioridazine is formed in appreciableamount. The maximum concentrations of THZ andits metabolites in the brain appeared later than inplasma. The peak concentrations and AUC values ofTHZ and its metabolites were higher in the brainthan in plasma corresponding to their longer half-lives in the brain as compared to plasma. The drugwas not taken up by the brain as efficiently asother phenothiazines. Chronic treatment with THZproduced significant increases (with the exception ofTHZ ring sulfoxide) in the plasma concentrations ofthe parent compound and its metabolites, which wasaccompanied with the prolongation of their plasmahalf-lives.17

Human metabolic pathway: Less than 1% is excretedin urine. Active metabolites for chlorpromazineare 7-hydroxy-chlorpromazine and possibly N-oxidechlorpromazine. Metabolites for THZ are numerousbut S-oxidation at the 5 position to more activecompounds (mesoridazine and sulphoridazine) isconsidered the main route.18

Safety and TolerabilityAnimal drug drug interactions: Imipramine (5 mg/kg)and amitriptyline (10 mg/kg) elevated serum levelsof THZ 20- and 30-fold respectively when adminis-tered to rats i.p. for 2 weeks. Increases of a similarmagnitude were found in the brain. Imipramineand amitriptyline also inhibited THZ metabolismresulting in an increase in the ratio of THZ to itsmetabolites. Cytochrome P450 was implicated inthese changes.18

Animal toxicity: Orally in rats, LD50 956 1034 mg/kg[DrugBank].Animal safety pharmacology: QT prolongation wasseen in anaesthetized guinea pigs with THZ.19

166 Thioridazine

Human drug drug interactions: CYP2C19 and espe-cially CYP2D6 are involved in the metabolism of THZ.THZ is also an inhibitor of CYP1A2 and CYP3A2.THZ use should be avoided in combination with otherdrugs that are known to prolong the QTc interval andin patients with congenital long-QT syndrome or ahistory of cardiac arrhythmias [DrugBank].Drugs that inhibit cytochrome P450 2D6 isozymeshould be avoided (e.g., fluoxetine and paroxetine);other drugs (e.g., fluvoxamine, propranolol, andpindolol) inhibit the metabolism of THZ and result inelevated levels adding to the potential for toxicity[DrugBank]. S-oxidation at the 5 position to moreactive compounds (mesoridazine and sulphoridazine)is considered the main route but oxidation at the5 position to THZ 5-sulfoxide, an inactive metabolite,also occurs.18

Human potential toxicity: THZ has been shownto prolong the QTc interval in a dose-dependentfashion. This effect may increase the risk of serious,potentially fatal, ventricular arrhythmias, such astorsade de pointes-type arrhythmias [DrugBank].There are many publications on the phenothiazinesand cardiac toxicity (reviewed in Kim and Kim200520) although many describe the most seriouscomplications, such as arrhythmias and suddendeath, as rare.20 The underlying cause for thesetoxicities is inhibition of the hERG channels; IC50s forinhibition of human hERG expressed in CHO cellsare THZ 224nM, perphenazine 1003nM, trifluorper-azine 1406nM and chlorpromazine 1561nM.20 THZ isnot generally considered to be the most toxic ofthe phenothiazines although its effect on cardiacfunction may be the most serious of the group(reviewed in Kim and Kim 200520 and Amaral et al.200121). Indeed THZ, considered a low-potencyphenothiazine, has been associated with numerouscases of “torsades de pointes” compared with otherdrugs in the class; perphenazine and trifluoperazine,considered high-potency, are considered safer asfar as cardiotoxicity is concerned (reviewed inKim and Kim 200520). The class has demonstrablehypotensive effects although these symptoms usuallyregress with continued dosing [Goodman & Gilman’s,pp. 497 8]; ironically, chlorpromazine has been usedto treat over 500 emergency cases of hypertension.22

Oxidation at the 5 position to THZ 5-sulfoxide, aninactive metabolite, is considered an issue as thismetabolite may contribute to cardiotoxicity. Therelatively similar MICs for these drugs21 perhapsindicate that the mechanisms for cardiac toxicity andbacterial killing are not identical and that an analogwith lower toxicity could be synthesized.Central nervous system side effects occur. These aremainly drowsiness, dizziness, fatigue, and vertigo.

THZ also causes an unusually high incidenceof impotence and anorgasmia due to a strongalpha-blocking activity. Painful ejaculation or noejaculation at all is also sometimes seen.Autonomous side effects (dry mouth, urinationdifficulties, obstipation, induction of glaucoma,postural hypotension, and sinus tachycardia) occurobviously less often than with most other mildlypotent antipsychotics.The serious and sometimes fatal blood damageagranulocytosis is seen more frequently (approxi-mately 1/500 to 1/1000 patients) with THZ than withother typical phenothiazines (1/2000 to 1/10,000patients).Human adverse reactions: Possible adverse eventsinclude agitation, blurred vision, coma, confusion,constipation, difficulty in breathing, dilated orconstricted pupils, diminished flow of urine, drymouth, dry skin, excessively high or low bodytemperature, extremely low blood pressure, fluid inthe lungs, heart abnormalities, inability to urinate,intestinal blockage, nasal congestion, restlessness,sedation, seizures, and shock [DrugBank].

References

1. Reddy M, et al. (1996) In-vitro and intracellularantimycobacterial activity of trifluoperazine. J AntimicrobChemother 37, 196 7.

2. Ratnakar P, Murthy P (1992) Antitubercular activity oftrifluoperazine, a calmodulin antagonist. FEMS MicrobiolLett 97, 73 6.

3. Yano T, et al. (2006) Steady-state kinetics andinhibitory action of antitubercular phenothiazines onmycobacterium tuberculosis type-II NADH-menaquinoneoxidoreductase (NDH-2). J Biol Chem 281, 11456 63.

4. Teisseyre A, et al. (2003) The voltage- and time-dependentblocking effect of trifluoperazine on T lymphocyteKv1.3 channels. Biochem Pharmacol 65, 551 61.

5. Vertessy B, et al. (1998) Simultaneous binding of drugswith different chemical structures to Ca2+-calmodulin:crystallographic and spectroscopic studies. Biochemistry37, 15300 10.

6. Boshoff H, et al. (2004) The transcriptional responses ofMycobacterium tuberculosis to inhibitors of metabolism:novel insights into drug mechanisms of action. J Biol Chem279, 40174 84.

7. Weinstein E, et al. (2005) Inhibitors of type IINADH:menaquinone oxidoreductase represent a classof antitubercular drugs. Proc Natl Acad Sci USA 102,4548 53.

8. Ordway D, et al. (2003) Clinical concentrations ofthioridazine kill intracellular multidrug-resistant My-cobacterium tuberculosis. Antimicrob Agents Chemother47, 917 22.

9. Kristiansen J, Amaral L (1997) The potential managementof resistant infections with non-antibiotics. J AntimicrobChemother 40, 319 27.

10. Rivarola H, et al. (1999) Thioridazine treatment modifiesthe evolution of Trypanosoma cruzi infection in mice. AnnTrop Med Parasitol 93, 695 702.

THZ

Thioridazine 167

11. Rivarola H, et al. (2002) Trypanosoma cruzi trypanothionereductase inhibitors: phenothiazines and related com-pounds modify experimental Chagas’ disease evolution.Curr Drug Targets Cardiovasc Haematol Disord 2, 43 52.

12. Weisman J, et al. (2006) Searching for new antimalarialtherapeutics amongst known drugs. Chem Biol Drug Design67, 409 16.

13. Xie Z, et al. (2004) Differential antibiotic susceptibilitiesof starved Mycobacterium tuberculosis isolates. Antimi-crob Agents Chemother 49, 4778 80.

14. Viveiros M, Amaral L (2001) Enhancement of antibioticactivity against poly-drug resistant Mycobacteriumtuberculosis by phenothiazines. Int J Antimicrob Agents17, 225 8.

15. Crowle A, et al. (1992) Chlorpromazine: a drugpotentially useful for treating mycobacterial infections.Chemotherapy 38, 410 9.

16. Bate A, et al. (2007) Synthesis and antitubercular activityof quaternized promazine and promethazine derivatives.Bioorg Med Chem Lett 17, 1346 8.

17. Daniel W, et al. (1997) Pharmacokinetics of thioridazine

and its metabolites in blood, plasma and brain of ratsafter acute and chronic treatment. Pol J Pharmacol 49,439 52.

18. Daniel W, et al. (2000) Pharmacokinetics and metabolismof thioridazine during co-administration of tricyclicantidepressants. Br J Pharmacol 131, 287 95].

19. Testai L, et al. (2004) QT prolongation in anaesthetizedguinea-pigs: an experimental approach for preliminaryscreening of torsadogenicity of drugs and drug candidates.J Appl Toxicol 24, 217 22.

20. Kim K, Kim E (2005) The phenothiazine drugs inhibit hERGpotassium channels. Drug Chem Toxicol 28, 303 13.

21. Amaral L, et al. (2001) Activity of phenothiazinesagainst antibiotic-resistant Mycobacterium tuberculosis:a review supporting further studies that may elucidate thepotential use of thioridazine as anti-tuberculosis therapy.J Antimicrob Chemother 47, 505 11.

22. Viskin S, et al. (2005) Intravenous chlorpromazine forthe emergency treatment of uncontrolled symptomatichypertension in the pre-hospital setting: data from 500consecutive cases. Isr Med Assoc J 7, 12812 5.

Tuberculosis (2008) 88(2) 168–169

TMC-207Generic and additional names: TMC-207; also known as R207910CAS name: 1-(6-bromo-2-methoxy-quinolin-3-yl)-4-dimethylamino-

2-naphthalen-1-yl-1-phenyl-butan-2-olCAS registry #: 654653-93-7Molecular formula: C32H31BrN2O2Molecular weight: 555.51Intellectual property rights: Johnson & Johnson has obtained patents for

this compound. Its subsidiary, Tibotec, is currently managing humanclinical trials of this compound.

N

N

Me

O

OHMe

Br

Me

Derivatives: 20 molecules in series have an MIC below 0.5 mg/mlFormulation and optimal human dosage: Reasonable bioavailability was found with oral solutions. Solid

formulations are under development. Oral administration achieved high in vivo activity.

Basic biology informationDrug target/mechanism: TMC-207 (R207910, TMC)is a first-in-class diarylquinone, distinct from anymarketed compounds. The compound, identified byscreening against Mycobacterium smegmatis, hasa unique mechanism of action (MOA) targetingthe c subunit of ATP synthase. ATP synthase isdivided into F0 and F1 multi-subunit complexes;F1 is cytoplasmic, F0 is membrane associatedand consists of a multimeric complex of pro-teins in the configuration a, b2, c9 12. The modeof action was identified through drug-resistantmutants harboring alterations in the atpE gene;this gene codes for ATP synthase c subunit, andchanges at D32V and A63P were associated withresistance.1 The compound did not inhibit gyraseactivity when tested against the purified enzyme,indicating that this molecule does not share MOAwith quinolones. Solid proof of the MOA comesfrom complementation of M. smegmatis with amutant atpE gene D32V rendering the normallysensitive wild-type strain drug resistant; followingthese complementation experiments the mutationD32V remained stable and no other changes werefound.1

Additional experiments to validate ATP synthasec subunit as the drug target include (a) overex-pression of the mutant target protein gene (atpE)in M. smegmatis leading to increased MIC for TMC;(b) demonstration of a dose-dependent decrease inATP in TMC-treated M. tuberculosis; (c) immobilized

TMC bound specifically and exclusively to M. smeg-matis ATP synthase subunits.2

Drug resistance mechanism: Spontaneous resistancerate for M. tuberculosis was 5×10 7 and 5×10 8

at 4× and 8× MIC respectively, similar to ratesobserved with rifampin (RIF).1 Mutants were un-changed in their sensitivity to RIF, isoniazid (INH),ethambutol (ETH), moxifloxacin (MOXI), strepto-mycin (STR) and amikacin (AMI). Mutations werefound in the atpE gene at D32V and A63P.1

Both mutations, in a highly conserved area, arewithin the membrane spanning region.3 No othermutation-related changes were found when thegenomes of the resistant M. tuberculosis and tworesistant M. smegmatis strains were sequenced tonear completion.1 No mutations were identifiedwithin gyrA and gyrB, demonstrating that TMCdoes not have the same MOA as quinolones.1

Complementation of wild-type M. smegmatis withthe mutant atpE gene D32V rendered the strain drugresistant.1

In-vitro potency against MTB: M. tuberculosis H37Rv:MIC 0.06mg/ml (0.03 0.12mg/ml).1

Spectrum of activity: TMC appears to be specific forMycobacterium, having activity against M. tubercu-losis, M. bovis, M. avium, M. kansasii, M. smeg-matis and M. ulcerans, significantly poorer activityagainst Corynebacterium and Helicobacter pylori,and essentially no activity against staphylococci,enterococci or Eschericia coli.1 The compound alsoshowed efficacy in a mouse leprosy model.4


TMC

TMC-207 169

Table 1


AUC(mg·h/l)

Cmax(mg/ml)


Clearance(ml/h)

PK methodology

Mouse 47*, 59** 5.0*, 19.4** 0.4*, 1.1** Single dose of *6.25 or **25 mg/kg1

Human 7.91, 24*, 52** AUCs for a once-daily dose at 50,*150 and **400 mg/day for 14 days.1

Other in-vitro activity: TMC is defined as bactericidalin vitro as demonstrated by a 3 log reduction inCFU after 12 days treatment of a log phase culture;no increase in activity was observed with a 10-foldincrease in drug concentration, indicating that killingwas time- and not concentration-dependent. TMC isactive against MDR-TB.1

In-vivo efficacy in animal model: TMC exhibitspotent early and late bactericidal activity. Oraladministration achieved high in vivo activity.“Non-established” mouse infection model: in micetreated 5× weekly for 4 weeks starting day 1 afterinfection, 50 mg/kg TMC was more efficacious than25 mg/kg INH, a drug known for excellent earlybactericidal activity. In the same model a minimaleffective dose (MED) of 6.25 mg/kg prevented grosslung lesions and 12.5 mg/kg gave 3 log reduction(bactericidal) in CFU in lung and spleen; the MED andbactericidal doses are very similar, suggesting killingis time-, not concentration-dependent.1

Persistent model: in mice dosed 5× weekly starting4 weeks after infection TMC (25 mg/kg) performedbetter than RIF alone and equal to standardcompounds RIF/INH/pyrazinamide (PZA). When TMCwas added to, or substituted for, any of thestandard compounds a greater decrease in CFUs wasobserved especially after 1 month of treatment.TMC has potential to shorten treatment time.1 Whencombined with second-line drugs used for treatmentof MDR-TB, namely AMI, ETA, MOXI and PZA, additionof TMC showed an improvement in activity includingsterilization of tissues from treated animals.5

Efficacy in humansIn clinical trials.

ADME dataSee table 1 for main PK characteristics.Other ADME data:• Mouse: 1:22 plasma: lung ratio, all other tissues

lower ratio but higher than in plasma. Half-life in

tissues ranged from 28 to 92 hours compared to44 64 in plasma.1

• Human: Peak levels were reached at 5.5 h(median). Average serum concentrations with aonce-daily dose at 50 mg, 150 mg and 400 mg/dayfor 14 days were 0.33mg/ml, 1.0mg/ml and2.2mg/ml respectively. “Effective” half-life is 24hours (suggested by data from multiple ascending-dose studies). PK was linear up to 700 mg (highestdose tested) with both AUC and Cmax increasinglinearly with dose; drug concentration in serumdeclined triexponentially.1

Safety and TolerabilityAnimal safety pharmacology: Preclinical safety indogs and rats together with genetic toxicology andgeneral safety pharmacology indicated that therewere no adverse events or toxicities precluding trialsin humans.1

Human adverse reactions: Repeated oral doses inhealthy human subjects showed no serious adversereactions when drug was administered at 50, 150 and400 mg daily for 14 days or up to 700 mg as a singledose.1

References

1. Andries K, et al. (2006) A diarylquinoline drug active onthe ATP Synthase of Mycobacterium tuberculosis. Science307, 223 7.

2. Koul A, et al. (2007) Diarylquinolines target subunit c ofmycobacterial ATP synthase. Nat Chem Biol 3, 323 4.

3. Petrella S (2006) Genetic basis for natural andacquired resistance to the diarylquinoline R207910 inmycobacteria. Antimicrob Agents Chemother 50, 2853 6.

4. Ji B (2006) Bactericidal activities of R207910 andother newer antimicrobial agents against Mycobacteriumleprae in mice. Antimicrob Agents Chemother 50,1558 60.

5. Lounis N (2006) Combinations of R207910 with drugsused to treat multidrug-resistant tuberculosis have thepotential to shorten treatment duration. AntimicrobAgents Chemother 50, 3543 7.

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